The hydration capacity of the roots grown in saline soil was less throughout than that of the roots grown in sand in which the salts introduced by the water of irrigation were much attenuated. Other differences suggest that the roots in the saline soi were more highly proteinaceous and also had a higher incorporated salt content.

Still another test was made with sections taken from the joints of Opuntia growing near the Desert Laboratory in February, 1921. The course of change in the chemical composition of this material is known in some detail. The pentosan constituent of the cellcolloids reaches a maximum earlier in the winter and was lessening at the time of the experiments but would still be so large as to make for a dominantly pentosan colloid. Swellings as in Table XIII were exhibited by two samples which are given in separate columns.

Swellings greater than in water are induced by KOH with a PH value of 12, in KC1 with a PH value of 5.7 and by HCl at 0.001 N with a PH value of 5.7.

Here as in all tests of living material the measurements are complicated by osmotic effects, although it is to be noted that the final swellings in Opuntia are reached after immersion for a day and the results are more clearly imbibitional than in any of the other material used.

GENERAL CONSIDERATIONS.

The following generalizations may be made upon the basis of the experimental results described in the foregoing paper.

I. The strong metallic bases which were found to lessen the swelling of agar to a degree corresponding to their relative posi

tions in the electromotive series when used as hydroxides, give the same relative action when used as chlorides. The series runs Ca, K, Na, the greatest retardation being effected by the calcium and the least by sodium, when used at concentrations of 0.01 M.

2. Reversed effects by which hydration of agar is increased are shown by the hydroxides at 0.001 N, as described in a previous contribution, but no well-defined differences among the bases used could be made out. Similar reversed effects were exhibited by the chlorides of calcium, magnesium, potassium and sodium at 0.0001 M and by potassium and sodium in concentrations as great as 0.001 M. 3. Purified agar used in the experiments has a PH value of 6.5, also swells more in HCl at a PH value of 4.2 than in water, a statement to be applied in correction of various conclusions in previous papers.

4. Purified agar shows exaggerated swellings in a series of acid, salt and hydroxide solutions in which the hydrogen ion concentration ranges from PH 4.2 to II.

5. Purified agar also shows exaggerated swellings in sodium and potassium nitrates at 0.0001 M but not in the sulphates.

6. Of the chlorides of calcium and potassium and hydrochloric acid at concentrations from 0.01 M to 0.0001 M only KC1 at 0.001 and 0.0001 M increase the swelling of an agar-gelatine mixture. In a similar series only KC1 at 0.0001 M increases swelling in a gelatine-agar mixture.

7. Agar plates with included chlorides at concentrations increasing swelling, when applied as hydrating solutions showed exaggerated swelling in HCl, NaCl, KC1 at 0.0001 M, but a lessened swelling in CaCl, and MgCl, at this concentration.

8. Gelatine plates with incorporated salts as above showed swelling in HCl increasing with the concentration beginning with the 0.001 M solution, in reverse of the action of the CaCl, solution which was greatest but still less than in water until at 0.0001 M. Swelling in KC1 did not exceed that in water until a concentration of 0.01 M was reached.

9. The maximum swelling of a gelatine (3 parts)-agar (2 parts) plate is greatest in HC1 0.01 N, KC1 0.001 M and CaCl, at 0.0001 M.

10. Different ecological types of roots of maize show different hydration reactions to the solutions used in hydration tests of colloids as noted in the foregoing paragraphs.

II. Roots of strawberry show differing hydration reactions when grown in saline soils and in sand.

12. Roots of orange seedlings show lessened hydration in acid solutions and their hydration was lessened in all solutions except balanced solutions of sea-water and of sodium and calcium chloride.

13. Swellings of sections of joints of Opuntia were greatest in KOH at 0.01 N, HCl at 0.001 N and KCl at 0.0001 M, all producing effects in excess of the swelling in water.

14. The changes in volume of living cell-masses in hydrating solutions include osmotic-plasmolytic effects in the alterations of the volume of the included cells. The hydration of dead cell-masses includes possible osmotic action of cell-walls.

15. The hydration reactions described in this paper may include coagulation effects when the higher concentrations were applied to the biocolloids, similar to those of the plasmatic colloids. Actual effects of balanced solutions are clearly defined in the hydration of agar, and some suggestions of similar action in the biocolloids arise from the measurements of swelling of the biocolloids described.

A NATURAL GROUP OF UNUSUAL BLACK OAKS.

(PLATES II TO IV.)

BY WILLIAM TRELEASE.

(Read April 21, 1921.)

Though most oaks bear only one or two acorns in a leaf axil, it is recognized generally that even when essentially sessile these fruits. and the flowers that produce them really pertain to a reduced pistillate catkin which is comparable with the staminate catkin. Sometimes the fertile flowers, though close together, are raised on a rather long peduncle, a condition well shown by our swamp white oak (Quercus bicolor) and the English oak (Q. pedunculata, or Q. Robur pedunculata). Several groups of Mexican and Central American white oaks have similarly long-peduncled acorns, e.g., those centering about Q. macrophylla, Q. peduncularis and Q. reticulata. In some of these, as in an exceptional ally of our own southern live oak Q. virginiana, occasional acorns occur along the peduncle; and in Q. decipiens of the eastern Sierra Madre these are frequent enough and the rachis is long enough to make the inflorescence in fact a sort of loose spike or catkin.

All of these belong to the section of white oaks, Leucobalanus, which are characterized technically by their short broad stigmas, basal abortive ovules, and the glabrate interior of the acorn shell.

The purpose of this paper is to make known three black oaks of the southern Mexican mountains which are quite unique in their section of the genus in bearing their fruit in racemes-or more properly spike-like clusters. They possess the technical characters of the black or red oak section, Erythrobalanus: elongated spatulate stigmas, subapical abortive ovules, and acorn shells tomentose within; but they differ from most black oaks and agree with all white oaks in maturing their fruit in the course of the season of

PROC. AMER. PHIL. SOC., VOL. LX, C, JULY 25, 1921.

flowering instead of deferring fertilization and maturation of fruit. for a year.

The first of these species was collected by Dr. J. N. Rose of the United States National Herbarium in the mountains of Tepic in 1897; the second, by Monsieur E. Langlassé in the Sierra of Michoacan or Guerrero in 1899; and the third, by Professor C. Conzatti of Oaxaca in the southern Cordillera in 1907. They constitute a natural group which in some respects suggests relationship with that embracing Q. crassifolia, Q. fulva and Q. stipularis, which likewise mature their fruit in the first season though differing greatly in some other respects. The common and differential characters of these new species may be stated thus:

Racemiflorae.-Moderately large trees with stout tomentose twigs, rounded buds, large cordate pandurate-obovate or orbicular concave aristately dentate petioled leaves impressed-veiny above and tomentose beneath, and small annual fruit in elongated raceme- or spike-like catkins, the thin cupules with tomentose scales.-Western Sierra Madre and southern Cordillera of Mexico.

Petioles long (20-30 mm.).

Leaves longer than broad, somewhat repand........ Leaves isodiametric, aristate from the nerves. Petioles short (scarcely 15 mm.): leaves isodiametric.

Quercus (Erythrobalanus) Urbani n. sp.

.Q. Urbani.

.Q. radiata

Q. Conzattii.

A tree 8-10 m. high, with tortuous trunk. Twigs stout, with dense yellowish tomentum persisting through the second season. Buds rounded, somewhat tomentose. Leaves large (15 x 16 cm.), deciduous, pandurate-subobovate, shortly acuminate, cordate-auriculate, lightly hollowed between the aristate ends of the veins, convex, glossy and glabrous except for the impressed veins above, densely creamy-tomentose beneath; petiole yellow-tomentose, 3x25 mm. Flowers unknown. Fruit annual, small, in yellow-tomentose spikes 80-110 mm. long, densely flowered toward the end; cup small (10 mm.), hemispherical, with thin appressed blunt fulvous-tomentose scales; acorn ovoid, 10 mm. long, canescent.

Called encino cucharilla, from its deeply spoon-shaped leaves. Western Sierra Madre of Mexico, at 1,800 m. (Langlassé, 1066, June 20, 1899), from Michoacan or Guerrero,-the type in the herbarium at Dahlem, for the privilege of studying which I am indebted to Professor Ignaz Urban, of that institution.