Exogenous Structure in Coal-Plants PROF. WILLIAMSON criticises my want of certainty with respect to the exogenous mode of growth of extinct Lycopodiaceae. But surely his reference to the Dixonfold trees does not prove more than that the diameter of their stems was greater near the roots than higher up. The same thing is true of many palms, but I think Pr. f. Williamson would be the last person to say that it was evidence of their being exogenous. Nevertheless, as I have already said, I am inclined to think that Prof. Williamson is right in supposing that the stems or extinct arborescent Lycopodiaceæ increased in thickness, although I do not see my way to asserting off hand that this was the case. Even admitting, with all Prof. Williamson's confidence, that it was so, I can see no classificatory value in the fact to justify overriding reproductive

characters in his new classification.

I said in my former letter (and the argument still appears to me a good one) that this increase was in any case nothing more than an adjustment to an arborescent habit dropped when the arborescent habit was lost." Prof. Williamson finds some difficulty in understanding this, and believes me to imply "that these exogenous conditions were merely adventitious growths assumed for a season and thrown off at the earliest opportunity; that they had no true affinity with the plants in which they were found." He confesses that he sees no ground for so remarkable a conclusion, and I may certainly say that as far as I comprehend

it, neither do I.

What I did mean to imply was, that in comparing the stems

of existing with those of extinct Lycopodiacea, allowance must be made for such adaptations of structure as would be likely to be correlated with enormous size. To make the matter clearer by an illustration :-Suppose we compare a nearly allied woody and herbaceous plant, say a lupin and a laburnum, we shall find in their stems (both "exogens") the same kind of diffe rences as exist between the stem of a herbaceous Selaginelia and that of the nearly allied arborescent Lepidodendron. The lupin may have had arborescent ancestors; if so, it has dropped all such adaptations of the structure of its stem to an arborescent habit as we find existing in laburnum. Assuming (what is of course only an assumption) that Selaginella is a descendant of Lepidodendron or its allies, the parsimony of nature has also sup pressed in it all those peculiarities of stem structure which were merely correlated with vast size, and in Selaginella and recent Lycopodiacea we have the residuum. In Isoetes, which is only 1 few inches high, there is a kind of lingering reminiscence of cir cumferential growth.

Prof. Williamson says that "herbs if they belong to the exogenous group are as truly exogenous in their type as the most gigantic trees of the same class. Size has nothing to do with the matter." With these statements I altogether disagree. I look upon the terms exogen, endogen, and acrogen as altogether obsolete from a classificatory point of view. Mohl pointed this out more than twenty years ago. Compare the following re marks from one of his memoirs with Prof. Williamson's: "The course of the vascular bundles in the palm stem and in the oneyear-old shoot of the dicotyledons is exactly similar, and the conception of a different mode of growth, and the division of plants into endogens and exogens formed on it is altogether opposed to nature."

66

Size, in fact, has everything to do with the matter. It is the persistent growth of the ends of the branches which makes the strengthening of the main stem by circumferential growth a mechanical necessity. Palms not being branched do not require the voluminous stem of an oak, and they exhibit on an enlarged scale only the structure of a one-year-old herbaceous shoot. But in the dragon-tree of Teneriffe an 'endogen," which becomes extensively branched, there is a true circumferential growth of the main stem, which increases pari passu with the development of the branches. All herbaceous stems, on the contrary, among flowering plants, whether belonging to the exogenous or endogenous group, have practically the same type of structure. Where is the exogenous type in the stem of the common artichoke, or in Ferula communis, figured by De Candolle in his "Organographie Végétale," pl. 3, fig. 3 "pour montrer à quel point elle simule les tiges de monocotyledones" (endogens)?

I think these remarks make it plain that circumferential (which is a preferable expression to exogenous) growth in stems is simply a necessary accompaniment of a branched arborescent habit. As far as the affinities of plants are concerned, it is purely acc dental and of no classificatory value. Lupinus being herbaceous and Laburnum arborescent does not prevent their being placed in the same tribe of a natural family. Since Mohl has shown that one-year-old (herbaceous) stems conform to the endogenous type, while such woody stems as Laburnum possesses are of course exogenous, it is clear that Prof. Williamson's views would overthrow all the work of modern systematists, and bring us back, as I pointed out in my former letter, to the primitive division of plants into trees and herbs (not trees and shrubs as Prof. Wil liamson makes me say).

The interpretation of the actual structure of the stems of the extinct Lycopodiaceae is of course another matter. Prof. William son illustrated his views at Edinburgh by referring to Lepidode dron selaginoides; every botanist who took part in the discussion, however, objected to his explanation. It may be true that this is only one form of such stems, but of course I can hardly be ex pe ted to be acquainted with the unpublished material which Prof. Williamson still has in hand. There is, I think myself, good reason for believing that Lepidodendron, Sigillaria, and Ulodendron all belong to a common type of stem structure; differences in fragments of different age of growth must be ex pected and allowed for. Of course, as I do not accept the existence of a pith in these plants, the pith or medullary ray must be rejected as well. Mr. Carruthers has shown, I think, conclusive reasons for disagreeing with Dr. Hooker with respect to the spaces which he identified with those structures. I was already familiar with the view of these s'ems taken by Prof. Williamson in his last paper. Those who are interested in the matter must judge for themselves who is right.

64

This communication has run on to so great a length that I am unable to touch upon other points in which I find myself totally disagreeing with Prof. Williamson. I cannot, however refrain from expressing my astonishment at the persistence of the histological views implied by the description of the "cambium," or growing cellular tissues of plants, as some protoplasmic element," or again as "some protoplasmic layer." Similar expressions were used by Nehemiah Grew about 200 years ago, and employed for some time by writers subsequent to him. the present I imagined their interest was wholly historical. W. T. THISELTON DYER

At

THE points at issue between Prof. Williamson and myself remain in the same position as at first. He has not yet answered one of my objections. He still holds that in Lepidodendron we have a vascular medulla, outside which is a series of fibrovascular bundles which are not closed, but go on forming new tissues by means of a cambium layer like a dicotyledonous stem. From my own observations, and from the study of recent Continental authorities, I have no hesitation in stating that the

central "medulla" of Prof. Williamson consists of the united closed fibro-vascular bundles, while the investing cylinder is the modified primitive tissue which increases in diameter by means of the meristem layer of Nägeli. If Prof. Williamson will refer to Sachs' Lehrbuch, Ed. 2, p. 397, he will find good reasons given for the statement there made, that Isoëtes contains no cambium in the stem; but that the stem increases in the same way as Dracena, i.e. by a meristem layer in the primitive tissue. long as Prof. Williamson believes in a central vascular medulla in these Lycopodiaceous stems, all his other conclusions must likewise be false.

As

W. R. M'NAB Royal Agricultural College, Cirencester, Oct. 21 {** We would suggest that this controversy be now closed, until the publication of Prof. Williamson's new material.-ED.]

Blood-Spectrum

IN the account of the Progress of Science in Italy in NATURE for October 12, Mr. W. Mattieu Williams says that Prof. C. Campani has shown that the spectrum of an ammoniacal solution of carmine is undistinguishable from that of blood, and that perhaps I should be able to tell whether any difference can be distinguished by more minute examination. In my first paper on this subject, so long ago as 1865*, I alluded to this similarity, and in subsequent papers + I have shown how the colouring matter of blood can be distinguished from that of cochineal, and even a small quantity recognised when mixed with a relatively considerable quantity of that dye. I have always argued that in such inquiries we must not rely on the spectrum, but compare the action of various reagents. On adding a little boric acid to an aqueous solution of blood, no change takes place in its spectrum, whereas that of cochineal is completely altered. This effect is not produced in the case of carmine suspended in water, but the absorption-bands of blood are at once removed by deoxidising the solution with a ferrous salt, which, on the contrary, has no effect in the case of carmine or cochineal. Weak acids decompose haemoglobin into hæmatin, which gives entirely different spectra, but they do not cause any permanent change in the colouring matter of cochineal or carmine. In my opinion there is no more probability of an experienced observer mistaking these substances for blood, because the ammoniacal solutions give nearly the same spectrum, than of a chemist confounding aluminium bronze with gold, because they are of nearly the same colour. H. C. SORBY

Broomfield, Sheffield, Oct. 23

Are Auroras Periodical?

THE following note on auroras is transcribed from the Iowa Instructor and School Journal for April, 1866. As it suggests a hypothesis similar to that proposed by Mr. Wilson, in your journal for September 7, it may not be destitute of interest. DANIEL KIRKWOOD

Bloomington, Ind., Oct. 4

"The Aurora Borealis of February 20, 1866 "Those who witnessed the grand auroral display of the 20th

*Quat, Fourn. of Science, vol. ii. p. 208.

Medical Press and Circular, New Series, vol. xii. p. 67; Monthly Micros. Journ., vol. vi. p. 15.

Besides the February epoch, any extended list of auroras will indicate two or three others, the most remarkable of which is that of November 13-18 (See Olmsted's paper in the Smithsonian Contributions,' vol. viii.) Fifty-three brilliant auroras have been observed since 1770. Of these, an accidental distribution would assign but one to the interval between the 13th and 18th of November; whereas eight of the number have actually occurred at that epoch. Are such coincidences accidental, or do they warrant the conjecture that, as in the case of shooting stars, there are particular periods at which the grand displays of the phenomenon most frequently occur?"

Forms of Cloud

THE form of cloud represented by Prof. Poëy in his figure a, in this week's NATURE, is very similar to that described by the Rev. C. Clouston, LL.D., in his " Explanation of the Popular Weather Prognostics of Scotland," published by A. and C. Black in 1867, and also in Dr. Mitchell's paper "On the Popular Weather Prognostics of Scotland," Edin. New Phil. Journal, Oct. 1863. Dr. Clouston says that, "when properly developed it was always followed by a storm or gale within twenty-four hours. It is called 'pocky cloud' by our sailors."

He gives a sketch from which, as he says, "it will be seen that this is a series of dark, cumulus-looking clouds, like festoons of dark drapery, over a considerable portion of the sky, with the lower edge well defined, as it each festoon or 'pock' was filled with something heavy, and generally one series of festoons lies over another, so that the light spaces between resemble an Alpine chain of white-peaked mountains. It is essential that the lower

edge be well defined, for a somewhat similar cloud, with the lower edge of the fe-toons fringed, or shaded away, is sometimes seen, and followed by rain only."

Dr. Clouston concluded his notice by saying, "this cloud is well known, and much dreaded by Orkney sailors." ROBERT H. SCOTT

Meteorological Office, London, Oct. 20

Elementary Geometry

IT is scarcely worth while for an anonymous writer to defend his opinions; but since a sentence in my letter of September 21 still continues to elicit remarks, I may be allowed to add an extaking in a subject, especially if it involves logical thought, explanation of my meaning. I stated that "no child is capable of cept by very slow degrees; and must at the beginning commit much to memory which he does not comprehend." And I called this "a fact." Mr. Wormell says in reply, that the purpose which geometry serves is not the exercise of the memory, and that it is useless if not understood. I entirely agree with him, and my words, if fairly interpreted, do not convey the contrary opinion.

In your last issue Mr. Cooley writes, that my principle, that a child must of necessity commit much to memory which he does not comprehend," appears to him totally erroneous, and not entit'ed to be called a fact. But surely the order of Nature with children is to possess themselves of empyrical knowledge by the exercise of memory, and subsequently to get to comprehend what they have thus acquired. Would Mr. Cooley wait until he had made a child comprehend the principles of the decimal scale, before he taught him to add up two rows of figures, and to say, "five and seven are twelve; put down two, and carry one"? If he condescends to the usual course of a "hearer of lessons" in this one instance, he acts upon the admission of my principle.

To apply this to geometry (and perhaps I may be borne with if I use Euclid in illustration): I fancy that many a boy at the beginning understands the three first propositions, but not the whole of the fourth. My plan would be, not to keep him at it till he did, but to let him learn it fairly well by rote, and go on, applying the results of the fourth by an act of faith. The second time he went through the book, if he had been decently taught,

As an entozoologist and correspondent of the Academy of Natural Sciences of Philadelphia, I request permission to correct an error recorded in the report of the Academy as given in your columns (at p. 500) this week. Dr. Leidy is represented as having stated that the minu e acetabular pit or fovea at the summit of the head [of Tania mediocanellata] is not mentioned by Kuchenmeister and subsequent observers as a character of that species.' I beg to remark that I both figured and described this supplementary sucker-like structure in the first edition of my small work on Tapeworms," published in 1866 (p. 33 et seq ). At least two other observers have figured and described this central depression, not only in the adult but also in the measle or cysticercal stage of the worm. Even Bremser recognised it, but his description was for a time overlooked.

84, Wimpole Street, London, Oct. 21 T. S. COBBOLD

Winter Fertilisation

IN the first number of NATURE, (for Nov. 4, 1869,) I ventured on a hypothesis, founded on a series of observations, that plants which flower in the winter have their organs of reproduction specially arranged to promote self-fertilisation. The following fact, which has just come under my notice, appears to confirm this theory. Plan's belonging to the order Caryophyllacea are, as a rule, strongly protandr us (see my paper in the Journal of Botany for October 1870), the anthers discharging their pollen at so long an interval before the maturing of the stigma as to render cross-fertilisation almost inevitable. The other day, Oct. 21, I came across a late flowering patch of Stellaria aquatica Scop., in which the anthers were discha ging their pollen simultaneously with the maturing of the stigmas, each of the five styles being curled in a singular manner round one of the stamens, so as to bring the stigmatic surface in actual contact with the dehiscing anther. This occurred in several flowers that were just opening, and there was abundance of seminiferous capsules on the plants. ALFRED W. BENNETT

Velocity of Sound in Coal

YOUR correspondent will find in Prof. Tyndall's beautiful work on "Sound" the data required for the exact determination of its velocity in different media. I believe that in coal it will be found to be between six and seven times that in air, or about 7,000 feet per second.

If Mr. D. Joseph places his ear against the solid coal of the "rib" or side of the "heading" or gallery, at a distance of some twenty to thirty yards from a collier at work, he will hear two sounds for each blow of the workman's pick or mandril-the first being transmitted through the coal, the second more slowly through the air, the impression being almost irresistible that two

persons are at work.

This is probably the origin of the legend, common in more than one coal district, of a collier who always worked alone, did more work than his fellows, and whose diabolical assistant was often heard but not seen. C. J.

Changes in the Habits of Animals YOUR correspondent Mr. Potts in the last number of NATURE furnishes us with a few interesting facts regarding the Kea. In a paper which I read about three years ago to the Dumfries Natural History Society, entitled "The Influence of the Human Period on the Sagacity of Animals," and subsequently in a letter published in NATURE, vol. i., on the "Mental Progress of Animals," I endeavoured to show from general considerations, and from the few facts which we possessed on this subject, that the habits and instincts of animals were not so fixed and definite as might be supposed. The general principle for which I contended was that whether we considered the globe to have received

its human inhabitants according to the laws of evolution, or in some miraculous manner, the arrival of the human race produced great modifications and changes of surrounding circumstances. These changes were in the direction of increasing the fertility of all vegetable productions capable of sustaining life, and at the same time securing their use entirely for the human family. Hence arose, in the vicinity of man, two new factors; the superior attraction of better food for all kinds of animals, and at the same time the extinction of such animals whose greed was not overruled by sufficient wariness or cunning to become successful thieves. Hence a probable gradual increase in these qualities in the animals maintaining themselves against man

Since my attention was drawn to this subject, we have had some interesting observations on modifications of swallow's nests by Pouchet, and a discussion as to the validity of his conclusions by Noulet, and now I have read with pleasure Mr. Potis's observations Most likely the progress of development in the carnivorous habits of the Kea will meet with a check now that shepherds are alive to its depredations; but without the influence of the human period we can scarcely suppose that such development would have begun. I recollect a case of change of habits in weasels They multiplied so thickly in a parish in the south of Dumfriesshire that some hungry philosopher among them took the initiative in sucking the blood from the cattle. Suspicion having been aroused, the fact was proved, but its discovery was fatal to the weasels, for the whole country-side arose against them, and all but extirpated them in that quarter. It is very interesting to observe what modifications are being produced in the haats of various species of sea-gulls since Glasgow, by its enormous increase of commerce, has wrought great changes in the River Clyde, filling it with all kinds of garbage. The conditions of existence having been favourable, the gull is steadily passing more and more time inland; ascending tributaries of the Clyde, and alighting in flocks on fields that used to have him very seldom. new amusement within my own recollection has been afforded the river passengers during the summer months in feeding these sea mews, &c., by throwing overboard food to them, and their increased tameness and boldness of approach in follow ing the river steamers within the last thirty years have been tre quently commented on. J. SHAW

A

THE words " aspect " and "slope" have already a use in re lation to the position of planes. They indicate two elements which together fix the position. Neither of them, taken alone, can indicate the position of a plane, unless a new and artificul meaning be assigned to one or other. Thus if I speak of the "aspect" of one of the faces of a roof as southerly, I have done something but not all that is necessary, towards describing the position of that face; if I add further that the "slope" is 30 ! have definitely assigned the position. Again if I speak of the "slope" of Saturn's rings as 28° (the plane of reference being ecliptic), I have done something towards the description of the position; if I add further that their "aspect" is toward sach and such a degree of the sign Gemini, I fully assign their po tion in space. And so on.

and

In the preceding sentences I have used the words " "slope" aspect" as they are already understood. I apprehend that ! have also used the word "position" as it is already understood, and that no other word could properly be used in the same sense in descriptive writing. I can see no reason why "peition" should be dismissed from the position it has so long courte nor why "aspect" and "slope" should be regarded in a sew and unfamiliar aspect.

It chances that I have long since had occasion to consider the question suggested last month by Mr. Wilson. In each of twelve books which I have written during the past six years, have had repeated occasions to consider the slope and assect that is, the " position" of many important astronomical plants.

I HAVE read with much gusto your article upon the Crystal Palace Aquarium. I am induced by it to put forward a caution with regard to the construction of rock-work in tanks.

Several weeks ago, casually looking over a heap of Bangor slaty rock, on the road bordering the Brighton Aquarium works, and being used for the rock-work of tanks, my attention was attracted by some bright green patches upon some of the stones, which appeared to me to be carbonate of copper, but was probably silicate. Looking further at one with a lens, I imagined that I could also distinguish particles of peacock ore. On attempting to purloin a specimen, I was very properly stopped from so criminal an act by the Cerberus in charge. I wrote to the chairman of the company, stating that, not having examined the stone, I might be only contributing a mare's nest to their zoological collection, but that if it contained much copper the fish would be in danger. I understand that upon receipt of my letter some rock was sent up to Dr. Percy, whose report, I am told, was to the effect that there was much sulphide of copper, and that the pretty green rock was therefore unfit for tank rock-work.

1 think this will serve as a caution to the constructors of aquaria carefully before using it. There are so many minerals which would be deleterious that I strongly advise an analysis and report in the case of every untried rock. The accident of my passing a heap of stones has saved the company, with which I am not in the least connected except as a fervent well-wisher, from a large expenditure and a serious scrape.

to examine all material which is to be in contact with water most

Allow me to ask those who are accustomed to the management of tanks, whether hydraulic pressure upon a small and strong one would be likely to assist in maintaining life in any of the deep-sea organisms, and whether it would be useful to make recesses for those loving darkness, with the axes opposite the plate glass side, so that a bull's-eye lantern could occasionally throw light upon their actions and mode of life? Brighton, Oct. 21

MARSHALL HALL

ON HOMOPLASTIC AGREEMENTS IN

AT

PLANTS

T the recent meeting of the British Association I pointed out in a short communication the difference that existed between mimicry in animals and what has been spoken of under that name amongst plants. The distinction was sufficiently obvious, and must have occurred to everyone who had given the matter any consideration, but my object was to try to raise a discussion upon the whole subject as exhibited in plants.

I fancy it is hardly sufficiently understood how commonly this agreement of facies occur in plants widely differing in other respects. I will give a few illustrations of it. Humboldt remarks ("Views of Nature," p. 351): "In all European colonies the inhabitants have been led by resemblances of physiognomy (habitus, facies) to apply the names of European forms to certain tropical plants, which bear wholly different flowers and fruits from the genera to which these designations originally referred. Everywhere in both hemispheres the northern settler has believed he could recognise alders, poplars, apple, and olive trees, being misled for the most part by the form of the leaves and the direction of the branches." Nor has the popular eye alone been deceived by these resemblances. Schleiden states ("The Plant," p. 255) that Australia has in common with Europe a very common plant, the daisy, yet Dr. Hooker has pointed out (Flora of Tasmania, pl. 47) that the plant intended by Schleiden is the very

similar but distinct Brachycoma decipiens Hook. fil. Again, true flowering plants belonging to the very curious family Podostemacea have been figured as liverworts and other cryptogamic plants (Berkeley, Intr. to Crypt. Bot., P. 5). Many other instances of similar errors might be given.*

Since I read my paper, I have met with an essay by Schouw, in which he enumerates facts of the same kind. "There is still," he says ("Earth, Plants, and Man," p. 61), "another kind of repetition which I might call habitual repetition, or denominate mimicry, if this expression was not at variance with the subjection to law which exists throughout nature, but to comprehend which our powers are often insufficient." After various illustrations he proceeds: In the genus Mutisia we have the remarkable sight of a compositous flower, with the tendrils of a leguminous plant." (This by an accidental coincidence was one of the instances which I, myself, used at Edinburgh.) "In Begonia fuchsioides the leaves are similar to a Fuchsia, and very different from the other forms of leaf among the begonias, and the colour of the blossom likewise reminds us of the fuchsias. We have another most striking example in certain Brazilian plants, which although possessed of perfectly developed flowers and fruits, mimic, as it were, in their leaves and stems, groups of plants of much lower rank.' (He is alluding to the Podostemaceae mentioned above.) "Lacis fucoides retaken for one by a person who did not see the flowers. sembles certain seaweeds so much, that it might be misMniopsis scaturiginum strikingly resembles a Junger

mannia."

I suggested that when a plant put on the characteristic facies of a distinct natural family, it might conveniently be spoken of as a pseudomorph, having in view an obvious analogy in the case of minerals. I do not, however, now think on further consideration, that this term, although convenient, includes all the cases. In small natural families it is not always easy to recognise any general habit different families where this is the case, but having a or facies at all, and in the case of plants belonging to similar habit, it would be purely arbitrary to fix the pseudomorphism on any of them. Again all the individuals of distinct groups of plants might have a similar habit, and the same remark would apply. The difficulty is, however, got over by speaking of the plants in these cases as isomorphic.

My friend, Mr. E. R. Lankester, has pointed out to me that agreements of this kind may all come under what he has termed homoplasy (Ann. and Mag. of Natural History, July 1870). This is the explanation he gives of this expression:

"When identical or nearly similar forces, or environments, act on two or more parts of an organism which are exactly or nearly alike, the resulting modifications of the various parts will be exactly or nearly alike. Further, if, instead of similar parts in the same organism, we suppose the same forces to act on parts in two organisms, which parts are exactly or nearly alike and sometimes homogenetic, the resulting correspondences called forth in the several parts in the two organisms will be nearly or exactly alike. I propose to call this kind of agreement homo plasis or homoplasy. The fore legs have a homoplastic agreement with the hind legs, the four extremities being, in their simplest form (e.g. Proteus, which must have had ancestors with quite rudimentary hind legs), very closely similar in structure and function. ... Homoplasy includes all cases of close resemblance of form not traceable to homogeny."

The resemblances, therefore, above described between the vegetative organ of plants with no close generic relations, may be described as homoplastic. The difficulty

having been published and described by Kunze as a species of Lomaria, a

* Perhaps one of the most striking is the Natal cycad Stangeria paradoxa genus of Ferns.

still, of course, remains to show how the homoplasy has been brought about. In some cases, as in the homoplastic forms of American Cactaceae and South African Euphorbias, or in the stipular bud scales of many wholly unrelated deciduous trees, the nature of the similar external conditions may possibly be made out with some correctness. Again, Dr. Seemann has pointed out that by the rivers in Nicaragua and in Viti, the vegetation, although composed of very different plants, puts on the willow form ("Dottings by the Roadside," p. 46). A phenomenon true of two distant places accidentally contrasted, might be expected to obtain more generally; at any rate, among our indigenous riparian plants Lythrum Salicaria and the willow-herb are, as their names indicate, additional illustrations. The band of vegetation that fringes a stream is always densely crowded with individual plants, and it is easy to see that elongated and vertically disposed leaves would be most advantageous, exactly as they are to the gregarious plants of meadows and plains. The homoplastic agreement of riparian plants may be therefore a direct result of selective effort due to the position in which they grow.

In other cases the operation of similar external moulding influences is not so easy to trace. It might, perhaps, however, be imagined that plants would hereditarily retain the effects when the influences had ceased to operate, and no new ones had come into operation precisely adapted to obliterate the work of those that preceded them. Suppose, for example, that willows got their habit and foliage from ancestors that were exclusively riparian, then any descendant that happened to be able to tolerate situations with less abundant supplies of moisture, would not necessarily lose their characteristic foliage on that account. Such races might be expected to occur near rivers subject to periodic droughts, since under these conditions any others would be likely to perish. Under such circumstances we should have cause and effect no longer in contiguity; the riparian habit surviving the riparian

situation.

I suggested at Edinburgh that possibly similar habits in plants might be bronght about by different causes. This was only a suggestion, and probably what has just been Isaid is a truer account of the matter. At any rate the illustration I gave of my meaning has been quite misunderstood (as, for example, in the last number of the Popular Science Review). It is well known that there are a certain number of plants indigenous to the British Isles, which are found at a considerable height upon mountains and also upon the sea-shore, but not in the intervening space. In the latter situations they contain more sodium salts than in the former, and inasmuch as these salts are destructive to many plants, those that compose a strand flora must be able to tolerate them, and this of course is an advantage, because many of their competitors are poisoned off. Similarly plants of mountains must have a similar advantage over others in ability to tolerate mountain asperities of climate. Now, suppose a mountain submerged; its flora and certain portions of that of the strand come to coincide. Then if we suppose the mountain gradually to emerge, some of these plants will spread downwards under the uncovered surface, and travel over the whole of the interval that ultimately separates the mountain-top and the strand. Why, then, do they not remain there? Simply, I believe, because they are elbowed out by other plants which, nevertheless,

cannot tolerate the conditions of life either on the moun

group of plants. Except as an illustration of this point, the matter was quite irrelevant to the subject about which I was speaking. W. T. THISELTON DYER

ON THE DISCOVERY OF STEPHANURUS IN

THE UNITED STATES AND IN AUSTRALIA

THE time has now arrived when a full statement of the facts relating to this interesting parasite. Stepha nurus dentatus, should be made more generally known; for not only is the progress of helminthological science likely to be checked by delay in this matter, but, in the absence of definite information, the several merits of the original discoverer and describer of this entozoon are likely to be altogether ignored. I therefore record the facts and inferences in the order in which they have recently come under my notice.

On the 10th of January last, through the firm of Mesir. Groombridge, I received an undated communication from Prof. W. B. Fletcher, of Indianapolis, Indiana, USA In that letter Dr. Fletcher announces that he has found a worm" infesting the hog, and he helps one to realise its abundance by adding that he obtained it "in nine out often hogs" which he examined. After recording some other important facts respecting the tissues and organs which were most infested by the parasite, Dr. Fletcher remarks that he cannot find any description of the worm in the work on Entozoa issued by the publishers above men tioned, nor in the writings of Von Siebold and Kuchenmeister, and he therefore encloses specimens for my determination, requesting a reply.

As I have already stated in my first letter recorded in the British Medical Journal (for January 14, P. 50, where many other particulars are given which I need not here recapitulate) I was instantly struck with the "strongyloid character" of the fragmentary and shrivelled up specimens, and I may also add that it at once occurred to me that! had had some previous acquaintance with a scientific description of the worm. Proceeding, therefore, to turn over a series of helminthological memoirs, for many of which I stand indebted to the late veteran, Dr. K. M Diesing, of Vienna, I soon had the good fortune to ind the desired record. The memoir in question forms part of the "Annalen des Wiener Museums" for 1839, the full title being "Neue Gattungen von Binnenwürmern, nebst einen Nachtrage zur Monographie der Amphistomen."

As this work is probably little, if at all, known in the countries now necessarily most interested in the history of this entozoon, I cannot, perhaps, do better than transcribe Dr. Diesing's brief notice of the original dis covery, together with his description of the external characters presented by the worm. After naming the parasite Stephanurus, on account of the coronet-like figure of the tail of the male, and giving a technical description of the species, he continues as follows:-"At Barra do Rio Negro, on the 24th of March, 1834, Natterer discovered this peculiar genus occurring singly or several together in capsules situated amongst the layers of fat, in a Chinese race of Sus scrofa domestica. Placed in water or in spirits of wine, they stretched themselves considerably, and almost all moved up and down."

rest. The tail of the male, when evenly spread out, is opposed to one another, are larger and stronger than the surrounded by a crown of five lancet-shaped flaps; the combined flaps being connected together from base to