ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 651 
cides with the region of greatest irritability. The attachment of a 
tendril to a support influences only in a minor degree the growth and 
formation of coils of the free portion of the organ. Such influence is 
due primarily to the traction exerted upon the organ by the weight of the 
shoot, not to a conduction of the contact stimulus. There are marked 
differences in the structure of the protoplasm of the convex and concave 
sides. The protoplasm of the concave side is richer in granules, and 
occupies a greater proportion of the cell-cavity, than on the convex side. 
The density of the protoplasm of the convex side increases from the base 
towards the tip, and apparently corresponds with the degree of irritability 
to contact. The parenchymatous cells of the concave side are markedly 
different in outline, structure, and form from those of the convex side. 
Motile Cushions of the Marantacese.* — Prof. S. Schwendener de- 
scribes the aquiferous tissue in the cushions which are found in the 
upper portion of the leaf-stalk of the Marantacese, and which often 
attain a considerable size. They are distinguished from similar organs 
in other plants by the possession of a peculiar tissue composed of cells 
which are elongated radially, or which have an oblique position. They 
are living cells with a nucleus and a contractile protoplasmic utricle, 
and contain cell-sap, which readily evaporates and is replaced by air. 
The motion of the leaf is dependent on the passage of water into and 
out of the cells. These cushions display also heliotropic curvatures, 
which bring the leaf into the most favourable position towards the in 
cident rays of light. This curvature does not appear, however, to 
originate in the aquiferous tissue, which bends only passively, the active 
seat of the curvature being the cortical parenchyme. The cushion 
possesses also an assimilating tissue and abundance of stomates. 
Turgor of Motor Organs.f — From experiments made on the motor 
organs of the leaves of some tropical plants, Dr. D. D. Cunningham asserts 
that their motility is not dependent on any specific contractility of their 
protoplasm, but on simply physical causes. It is connected with the 
composition of the cell-sap ; turgor may be manifested in cells where 
the cell-sap is not enclosed in a continuous protoplasmic sac, or where 
the protoplasm has been killed. The protoplasm has, however, an 
indirect influence on turgor, by bringing about the production of osmotic 
conditions in the cell-sap. The simplest examples of nvctitropic 
movements are the opening and closing of the stomates. Ordinary 
nyctitropic movements are determined, not only by the conditions of 
illumination, but also by the daily varying relationships between the 
absorption of water and transpiration. 
Geotropism and Heliotropism.J — Dr. F. Czapek gives the result of 
a series of experiments on the combined effects of geotropism and helio- 
tropism on plants. He finds that when strongly sensitive plants or 
organs (seedlings of Avena or Lepidium) are placed horizontally for 60 
or 80 minutes, until an upward geotropic curvature of the apex has 
* SB. K. Preuss. Akad. Wiss. Beilin, 1896, pp. 535-46 (1 pi.). Cf. this 
Journal, ante , p. 439. 
f Ann. R. Bot. Garden Calcutta, vi. (1895) 161 pp. and 7 pis. See Bot. Gen- 
tralbl., Ixvii. (1896) p. 141. % SB. Iv. Akad. Wfis. Wien, civ. (1895) pp. 337-75. 
