ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
771 
conclusions are arrived at: — (1) Species of Umbellifene with greatly 
divided leaves assimilate more, for an equal surface, than those with 
entire or less divided leaves. (2) This difference in the intensity of 
the assimilation is explained by the disposition of the palisade tissue, 
which, instead of being in a single layer, may consist of several super- 
posed layers. 
Assimilation of free atmospheric Nitrogen.* — Dr. R. Otto gives a 
resume of the results of the more important investigations on this subject 
from the time of de Saussure at the commencement of the century to 
the present time. 
Absorption and Metabolism of Fatty Oils.j — Herr R. M. Schmidt 
has carried out a series of experiments for the purpose of determining 
in what way the fatty oils contained in many seeds are employed in the 
nutrition of the young plant. The experiments made on the absorption 
of almond-oil by mould-fungi and by the cells of higher plants, appear 
to indicate that the passage of such oils through living cellulose mem- 
branes is the result of a saponification caused by the combination of a 
substance present in the cell- wall with the free fatty acids. It is 
possible also that a direct passage of the oil from cell to cell may take 
place, since the parietal utricle is permeable for oils ; and in the germina- 
tion of oily seeds, observation has not at present shown that any large 
quantity of free fatty acids is produced; these are apparently formed 
only at a comparatively late period. 
(3) Irritability. 
Anatomico-physical causes of Hygroscopic Movements. :j: — Herr C. 
Steinbrinck has undertaken an investigation of the mechanical causes 
of the hygroscopic movements which bring about the bursting of 
mature capsules and pollen-sacs. The hygroscopic tension may be 
produced mainly by the normal shrinking either of layers or of striae ; 
to the former type belong the capsules of Linaria, Antirrhinum , and 
Helianthemum , and the pollen-sacs of the Cycadeae ; to the latter class 
the capsules of Luzula and of the Caryophylleae ( Dianthus , Saponaria, 
Silene, Gypsophila , and Spergula) ; those of Lychnis vespertina show 
an intermediate structure between the two. The details of the structure 
are described in the various species examined. 
Irritability of the Leaves of Dionsea.§ — According to Mr. J. M. 
Macfarlane, all parts of the lamina of the leaf of Venus’s fly-trap are 
sensitive to surface stimulation. For mechanical stimulus of the leaf 
two touches are needed to cause contraction, unless the stimulus be very 
powerful, and they must be separated by a greater interval than one- 
third of a second. If less than one-third of a second elapses there is no 
contraction, and a third touch is then needed. In the first case no effect 
is produced if 35-40 seconds elapse between the stimuli. The author 
claims a perfect parallelism between combined nerve and muscular 
action in animals and contractive action in Dionsea. 
* Bot. Centralbl., xlvi. (1891) pp. 387-91 ; xlvii. (1891) pp. 62-7, 123-9, 175-90. 
f Flora, lxxiv. (1891) pp. 300-70. J Tom. cit., pp. 193-219 (1 pi. and 1 fig.). 
§ Bot. Gazette, xvi. (1891) p. 258. 
