duce of Hope's plant, are-1. that the leaves, identical in form and size, instead of being bright grass-green, have a dusky-green hue; 2. that the back of the leaf, of a light grey colour, is covered with minute hairs, which in Hope's plant are confined to the venations; 3. that the petioles, instead of green, are purple; 4. that the stem is purple, but in Hope's plant presents only small interrupted purple streaks; and 5. that the panicles in the latter are more branchy and wide-spreading than in the new plant. These differences are slight. The last difference is plainly owing to the greater age of Hope's plant, which is an old one; for in his drawing of his two-year-old plant there is not the slightest departure from the form of the panicles in that of Prejevalsky, as now presented in the Botanic Garden. It is here necessary to remark that in a very pretty drawing, contributed to that traveller's book by Professor Maximinovitch, the flowers are represented as forming, not branched panicles spreading out from the stem, but rather separate spikelets, without the slightest ramification, and rising parallel to the stem, and close to it. This might be an important difference, were it exact or uniform. But assuredly in the new plant in the Botanic Garden, when in full flower, the inflorescence consists of panicles much ramified, and spreading out from the stem. It may be remarked however that three days later, when the fruit had begun to set, the flowers of each peduncle became appressed into the resemblance of an unramified spike, and the peduncles themselves almost parallel to the stem; so that the whole plant had exactly the same appearance as in Prejevalsky's drawing; and the same change took place at the same time in the progeny of Hope's plant.

The differences here noted obviously do not constitute a difference of species between the plants of Hope and Prejevalsky. They are indeed scarcely enough to establish the latter as a probably permanent variety of the former. Nevertheless it may be admitted meanwhile as such, under the name of Rheum palmatum Tunguticum, assigned to it by Maximinovitch.*

Dr Hope expressed a decided opinion that his plant was The principal plant has now (July 18) very nearly ripened numerous seeds; so that there is no doubt of its propagation in this climate.

*

the source of the finest rhubarb,-then called Turkey rhubarb, because imported into this country from the Turkish ports, and more recently Russian rhubarb, because imported from the eastern confines of China by way of Siberia and St Petersburg. He says-" Although the root was taken up a great deal too young, and at an improper season (viz., in July), yet it had most perfectly the smell of the true rhubarb; and when chewed, though it was at first soft and mucilaginous, it soon discovered exactly the taste of the best foreign rhubarb. I have made trials of the powder of the root in the same doses in which the foreign rhubarb is given, and found no difference in its effects, its operation being equally easy and powerful."

This is strong testimony; and Hope was well entitled at the time to add that "from the perfect similarity of this root with the best foreign rhubarb in taste, colour, smell, and purgative properties, we cannot doubt of our being at last possessed of the plant which produces the true rhubarb, and may reasonably entertain the agreeable expectation of its proving a very important acquisition to Britain." Prejevalsky's discovery, and the botanical characters of his plant as cultivated here, raise the question, whether Dr Hope's expectation may not be now revived. That expectation has been by no means hitherto fulfilled. For it is well known that for many years rhubarb, considerably resembling Russian rhubarb in external characters, but decidedly inferior to it as a remedy, has been largely and profitably cultivated at Banbury in Oxfordshire; but that Hope's Rheum palmatum has not been found to yield there a marketable British rhubarb; that various species of successive introduction to botanical science from Central Asia have been tried in their turn; and that all have proved failures except one, which has been identified as Rheum rhaponticum, the species earliest known in Europe, and not, so far as we are yet aware, a native of the rhubarb district of Mongolia. For most of this information we are indebted to Dr Pereira, after careful inquiry in communication with the Banbury cultivators. The testimony of one

of them is to the effect that "no other species was ever cultivated at Banbury, and that he cannot produce British rhubarb from the giant-rhubarb or any other sort [“Ele

ments of Mat. Med." ii. 1354]. In France no greater success has attended the cultivation of two other species, Rh. compactum and Rh. undulatum."

But have these trials to introduce the culture of true fine rhubarb been made under suitable conditions?

Of

Here we are at once confronted with the question, Are the plains of France or of Oxfordshire the proper locality for cultivating a plant whose native habitat is the narrow valleys of a mountainous country, 10,000 feet above the sea, and in 37° north latitude? Clearly not. From what is known of the influence of locality on many plants, important differences in property may well be expected to arise from so very great a deviation from nature's rule. course we cannot secure anywhere in this island all the conditions of the native country of the Rh. palmatum Tunguticum. But something much nearer surely may be attained than any locality in the southern plains of England can supply. It is only too clear that in this neighbourhood we can command, in most years at least, the cold ungenial spring, which Hope's success, and the perfection of the plant now flowering in the Botanic Garden, prove to be most grateful to the Rh. palmatum. But we cannot ensure the very hot summer to which it is accustomed in its native soil, and to which it may be indebted both for thorough ripening of the seeds, and also for the root abounding duly in its purgative principle.

Prejevalsky informs us that his plant thrives in an extensive district in the neighbourhood of the town of Chobsen, in north latitude 37° 3′ and 100° 58′ east longitude, on one of the northern source-tributaries of the Hoang-ho river, and around the great lake Koko-nor, about eighty miles farther west. Its favourite locality is the narrow valleys or ravines at the basis of snow-capped mountains, at an elevation about 10,000 feet, and with an exposure towards the north; and it is little seen on the sides of the same valleys facing the south. It seemed to grow best in a deep black mould. The waters of the district where it abounds are impregnated to an unusual degree with lime; which he thinks ought not to be lost. sight of in any attempt to cultivate it. Fine Russian rhubarb-root contains a very large proportion of oxalate of

lime in crystalline groups; and one of the most remarkable differences between fine Russian rhubarb and British rhubarbs is the want of these crystalline masses in the latter. Moreover, the prevalent Tungutan flora seems to approach closely to that of the hilly parts of Europe and of this country. Prejevalsky enumerates among the leading genera-Abies, Aconitum, Ajuga, Allium, Anemone, Berberis, Betula, Cratægus, Epilobium, Fragaria, Gentiana, Lilium, Myosotis, Orobus, Oxytropis, Pedicularis, Pinus, Polygonum, Populus, Potentilla, Primula, Prunus, Pyrola, Ranunculus, Ribes, Rubus, Rumex, Sambucus, Senecio, Taracetum, Thalictrum.

The statement of Pereira, that all species had failed to produce at Banbury a root like commercial rhubarb except Rh. rhaponticum surprised me; because ten years before the publication of his work, viz., about the year 1840, the late Professor Graham and Mr Macnab, sen., supplied me with large roots of old plants of eleven species, cultivated in the Botanic Garden, among which were Rh. palmatum, undulatum, compactum, emodi, and rhaponticum; and I found that the only one which dried into a root resembling commercial rhubarb was Rh. palmatum. Pereira in England, and Guibourt in France, afterwards made a similar set of trials, and with the same result.

On the whole, I have a strong opinion that the cultivation of the plant of Hope or Prejevalsky well deserves to be repeated in circumstances different from those attending the experience of the Banbury cultivators; that the most feasible locality would be some deep-soiled terrace at the southern border of our Highland mountains, such as in Strath-Tay or Strath-Earn; and that attention should be paid to what Prejevalsky has said of the native locality of the plant, with the single exception that in our land a southern may be prudently substituted for a northern

exposure.

I am quite aware that French naturalists have recently attempted to prove that the best rhubarb is obtained from a totally different species, new to science, called Rheum officinale, a huge, coarse, many-stemmed sort, which is also in cultivation, and on the point of flowering (June 7th), on the terrace in front of the long range of hot-houses in our

Botanic Garden. It is no part of my present intention, nor indeed have I any desire, to call in question the right to assume this very widely different species to be the true rhubarb plant, by calling it Rh. officinale.* But no one, who peruses the admirable work of Prejevalsky, can entertain any doubt of his having ascertained on the spot the fact, that his plant supplied that kind of rhubarb, which till 1870 used to be transported to the border Chinese town Miamatchin, for transference over the border to Kiachta, and thence across the Siberian continent to St Petersburg, as the finest or Russian rhubarb, and which has ceased to appear in commerce, under that name, or from the Russian capital, since the rebel Dungans overran the rhubarb country of the Tunguts, and put an end to their commercial communications northwards.

IV. The Exact Measurement of Trees.
Yew Tree. The Fortingall Yew.
CHRISTISON, Bart.

(Read July 1, 1879.)

(Part 3.)—The By Sir ROBERT

In the last remarks on the applications of the minute measurement of the trunks of trees an attempt was made to fix, so far as may be accomplished by the measurements of a single year, the rate of growth of the adult beech and the young Sequoia. The object of the following inquiry is a more ambitious one, and much more difficult to attain, viz., the rate of growth of the yew at various ages; and a leading application of this inquiry is to determine, if possible, the age of the Fortingall yew, which has been credited with an antiquity far beyond that of any other tree in Britain, and has been thought indeed by no less an authority than De Candolle to be possibly "the most venerable specimen of vegetation in Europe."

It must be mentioned in the first instance that the common yew [Taxus baccata] puts on two different forms,

Aug. 1.-The Rh. officinale here is now a plant whose foliage covers a space 8 feet in diameter and 6 feet high; and it has produced seven flowering stems 10 feet in height, besides many not so tall. Some of the flowers have formed well-advanced fruit. Its flowering season seems much later than that of Rh. palmatum.