ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 55 



of Stahl and Haberlandt, who have explained differentiation of the 

 lnesophyll of an ordinary dorsiventral leaf into an upper palisade and a 

 lower spongy layer as an adaptation to favour photosynthesis, and at the 

 same time to ensure the protection of the chlorophyll-corpuscles. The 

 author finds that with dorsiventral leaves photosynthesis is reduced if 

 the lower surface is illuminated by direct sunlight instead of the upper. 

 The greatest difference is found in thick leaves ; e.g. in cherry laurel the 

 proportion was as 100 to 48. In leaves where the mesophyll is more or 

 less homogeneous, as in the bamboo, the difference was small, the pro- 

 portion being 100 to 92. 



E. 0. Herzog * finds that extracts prepared from crushed green 

 leaves by the method used by Buchner to extract the ferment from 

 yeast have no power to absorb carbon dioxide and give out oxygen. 

 This confirms the view that the photosynthetic power of the chlorophyll 

 corpuscle is dependent on the life of the protoplasm. 



Assimilation of Yeasts.f — Th. Bokorny, of Munich, has studied 

 the effect of the environment on the life of the yeast plant. He made 

 a series of experiments on the influence of temperature, and he found 

 that while 35° C. was too warm, 5° C. was too cold for healthy develop- 

 ment. At the lower temperature the weight of the plant decreased. 

 This result coincides in some measure with that determined by Kreusler 

 for green plants ; 20° was found to be more favourable than 35°. Cold 

 did not, however, affect so seriously the green plant experimented with. 

 The writer tested also the effect of various concentrations of fluid, to 

 some of which poisons or otherwise harmful substances were added. In 

 most of the experiments a 20 p.c. solution of cane-sugar was used, but 

 the highest degree of activity was reached with 5 p.c. The greatest re- 

 tardation resulted from the introduction of minute quantities of caffein. 

 Fluoric acid was found to be almost equally hurtful. Free phosphoric 

 acid was also found to act as a check. 



Irritability. 



Influence of Light on Seed-Gennination4 — E. Heinricher has 

 studied the relation of light to the germination of seeds in a number of 

 genera and species. In the case of many plants which inhabit strongly 

 insolated localities light seems to exercise a very important influence on 

 germination ; but the rule is not general, as certain light-loving plants, 

 such as species of Mesembryantliemum and others, germinate as rapidly 

 and as well in the dark as in the light, and in some cases, as in the 

 Bromeliad Acanthostachys strobilacea, darkness favours germination. 

 Seeds of Pitcaimia maidifolia and Drosera capensis, on the other hand, 

 refused to germinate in complete absence of light ; such a strongly- 

 marked influence of light has been known previously only in the case of 

 the mistletoe. The author suggests that the same relation holds in the 

 case of other plants, especially light-loving epiphytes of the savannas; 

 most of the Tillandsiese probably resemble Pitcaimia maidifolia in this 



* Zeit. Physiol. Chem., xxxv. (1902) pp. 459-64. See also Journ. Cbera. Soc. 

 lxxxii. (1902) ii. p. 578. t Centralbl. Bakt., ix. (1902) pp. 55-62. 



% Beih. Bot. Centralbl., xiii. (1902) pp. 164-72. 



