ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
593 
Ascent of Sap. — Fresh experiments by Prof. S. Scliwondener * con- 
firm his previous statement that the action of suction and of root- 
pressure does not extend to the middle part of the stem of trees. The 
movements of sap nevertheless take place without interruption in this 
portion of the stem, and must be due to forces of a special nature which 
are not yet fully known, but which play an important part in the life of 
plants. 
Prof. E. Strasburger f replies at great length to Schwendener’s 
criticisms on his previous conclusions, for which he now adduces further 
evidence, especially insisting on the point that the co-operation of living 
cells is not necessary for the ascent of sap in plants. 
(3) Irritability, 
Irrito-contractility.J — Prof. J. M. Macfarlane has extended the ob- 
servations already made on Dionsea to other sensitive plants, and draws 
from them the following conclusions : — In the vegetable, as in the animal 
kingdom, we have to do with a true contractile tissue. In the higher 
plants this tissue is made up of cells, each consisting of an irrito-con- 
tractile protoplasmic sac enclosing a quantity of sap, and each cell joined 
to neighbouring cells by protoplasmic processes which pass through 
minute pores in the common cell-wall. 
Irrito-contractility may be started by stimuli of a mechanical, 
chemical, thermal, luminous, or electrical nature. For the movements 
of the leaves of Oxalis and Mimosa , called by Darwin paraheliotropic, 
the author proposes the better term parathermotropic , since they are 
caused not by differences of light, but of temperature. In the case of 
mechanical stimuli, two successive ones are usually necessary to start 
contraction. 
The phenomena of contractility are described in detail in a number 
of sensitive plants, species of Oxalis, Mimosa , Cassia , Amjphicarpsea, Des- 
modium , &c. The seat of this contractility is unquestionably the vacuo- 
lated protoplasm, and not the cell-wall. A similar sensitiveness to 
impact is possessed also by growing tendrils, notwithstanding the asser- 
tion of Pfeffer to the contrary ; and the tentacles of Drosera are, like 
tendrils, sensitive to contact as well as to impact. The degree of con- 
traction of an organ is proportional to the relative molecular activity of 
the protoplasm, and to the strength or continuity of the stimulus. 
(4) Chemical Changes (including Respiration and Fermentation). 
Storing up and Transport of Starch.§ — From observations made in 
Java, Mr. J. C. Oosterus states that, in the case of shrubby plants and 
those not of great height, where the leaves are exposed to the sun during 
the whole day, they contain the largest quantity of starch an hour before 
sunset or earlier ; about this time the transport of starch is more ener- 
getic than assimilation, while at sunset the latter is altogether suspended, 
and the slow transfer of starch begins to the places where it is consumed. 
* SB. Akad. Wiss. Berlin, Oct. 26, 1893. See Bot. Centralbl., lvii. (1894) p. 135. 
Cf. this Journal, 1893, p. 355. f ‘ Ueber das Saftsteigen,’ Jena, 1893, 94 pp. 
X Biol. Lectures delivered at the Marine Biol. Lab. of Wood’s Holl, Mass., 1893 
(1894) pp. 185-209. Cf. this Journal, 1883, p. 357. 
§ Ann. Jard. Bot. Buitenzorg, xii. (1894) pp. 73-90. 
