ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
639 
reservoirs of food-material. The tubercles are formed, not at the base 
of the stem, but in a region commencing with the fourth internode, and 
extending upwards for a space of five or six internodes. A tubercle thus 
formed, when placed in the soil, puts out numerous roots, and, at its 
apex, a kind of rhizome ; from this is developed a secondary tubercle, 
which bears the flowering stem. 
Dissemination of the Polygonacese.* * * § — Herr U. Dammer describes 
the various contrivances for promoting the dissemination of the fruits 
and seeds of the different genera of Polygonaceae ; and the vegetative 
propagation by means of stolons or gemmae, such as those in the 
inflorescence of Polygonum viviparum . The dissemination of the fruits 
is assisted especially by membranous wings, by bristles, and by callo- 
sities on the persistent perianth-leaves. The number of these callosities 
is two or three in those species where the fruit is carried by running 
water, so that it lies flat on the surface, but only one in those in which 
the fruit falls into stagnant water. Pumex and Oxyria are anemo- 
philous, while Rheum is entomophilous. 
Relationship between the Concentration of the Substratum, and 
Turgor and Growth. | — Herr B. Stange has investigated this subject in 
the case of some flowering plants, especially Phaseolus vulgaris , Pisum 
sativum , Lupinus luteus, and Cochlearia officinalis. He finds that in 
accordance with previously recorded observations on the lower plants, 
flowering plants can also adapt themselves to a higher degree of con- 
centration of the substratum, and this is accompanied by an increase in 
the osmotic pressure within the cell. The osmotic processes are more 
or less connected with the action of light. In the dark the osmotic 
pressure is less, even with an increased concentration of the substratum. 
Influence of Nutriment on the Vegetable CelLJ — Dr. T. Bokorny 
gives the result of a series of experiments on the changes effected on the 
form and growth of the cell — chiefly Spirogyra — by supplying it with 
different nutrient media. These changes affect the form and length of 
the cell, the extent to which the filament branches, the position, breadth, 
and colour of the chlorophyll-bands, the amount of starch they contain, 
the proportion of proteids in the cytoplasm, and the composition of the 
cell-sap, especially as to the amount of tannin contained in it. 
Biology of Buds.§ — Dr. J. Griiss has investigated the structure of 
the leaf-buds in a number of trees, both evergreen and deciduous, and 
the functions which they perform. In many trees the parenchymatous 
cells of the outer covering of dormant buds serve as a reservoir for 
food-materials, chiefly carbohydrates. But the chief function of this 
covering is as a protection against excessive transpiration ; the pro- 
visions for this purpose consist in an excretion of resin, and the forma- 
tion of layers of cork or of a hairy coating. Protection is also afforded 
by the same contrivances against a sudden fall of temperature. The 
special structures are described in detail in a number of examples. 
* Biol. Central bl., xii. (1892) pp. 257-61. 
t Bot. Ztg., 1. (1892) pp. 254-9, 273-9, 292-301, 305-12, 329-33, 342-50, 363-7, 
373-9, 394-400, 409-13, 429-32, 446-50. 
X Biol. Centralbl., xii. (1892) pp. 321-30. 
§ Jahrb. f. Wiss. Bot. (Pringsheim), xxiii. (1892) pp. 637-703 (4 pis.). 
