370 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
species of Cucurbita. The following are his more important conclusions. 
Increase in size or in weight is either continuous, or is interrupted bv 
periods of loss in weight or shrinkage in diameter. Both increase and 
decrease may take place at the rate of 0*1 grm. per minute in weight, 
and of 0*01 mm. per minute in diameter. Variations in the rate of 
growth are chiefly dependent on the hygrometric condition of the atmo- 
sphere, increased humidity causing increased growth, and vice versa. 
Changes in the amount of light have but little effect. Syringing the 
leaves and watering the soil cause a rapid increase in growth. The 
curve of growth shows a minimum in the afternoon, followed by a rapid 
rise towards evening, and this is followed by a fall as the night proceeds. 
The rate of growth is more uniform by night than by day. 
Metastasis and Respiration in Germinating Tubers and Seeds.* — 
Herr E. Ziegenbein records the results of a series of experiments on 
germinating potatoes and seeds of Lupinus luteus and Vicia Faba, from 
which he derives the following conclusions. Free oxygen is not neces- 
sary for the breaking up of protoplasm in the living plant ; nor is light 
necessary for the same purpose in the potato. Variations of tempera- 
ture up to 30° C. have no effect upon the rapidity of germination ; a 
still higher temperature (42°-43-5°) acts prejudicially on germination. 
The optimum temperature for respiration varies, for different plants, be- 
tween 35° and 40°, The production of carbon dioxide goes on at tem- 
peratures below the freezing-point. 
Transpiration of Succulent Plants, j — Dr. F. Noll describes an 
experiment by which he demonstrates the relation between the transpi- 
ration of a typical succulent ( Fchinocactus ) and a typical non-succulent 
plant (leaf of Aristolocliia Sipho). Comparing similar weights, the 
transpiring surface is 300 times greater in the latter than in the former 
case. Taking now Opuntia instead of EcJiinocactus, it was found that, 
for a unit of surface, the amount of transpiration was 17 times greater in 
the herbaceous than in the succulent plant. It follows that, for the 
same weight of substance, the amount of transpiration is 5100 times 
greater in a thin-leaved than in a succulent plant. 
C3) Irritability. 
Irritability.J — Prof. W. Pfeffer defines irritability as the phenomena 
produced by the “ release ” ( Auslosung ) process following after any 
impact. He regards the faculty as a fundamental property of all living 
organisms, whether animal or vegetable. The most recent researches in 
this department of physiology are referred to in detail. The sensitive- 
ness of bacteria and of the antherozoids of ferns and mosses is so delicate, 
that the trillionth part of a milligram, say of malic acid, or of sugar of 
milk, will exercise a sensible attractive force. 
Geotropism and Epinasty.§ — Dr. F. Noll describes a modification 
of the clinostat by means of which he has determined that the strong 
.median curvature which takes place in the flower-stalk of dorsi ventral 
* Juhrb. f. wiss. Bot. (Pririgsheim), xxv. (1893) pp. 563-606. 
' Flora, lxxvii. (1893) pp. 353-6. 
't Verhandl. Gesell. Deutsch. Naturf. u. Aerzte, 1893, 31 pp. See Arch. Sci. 
Ph'ys. et Nat., xxx. (1893) p. 397. § Flora, lxxvii. (1893) pp. 357-62 (1 fig.). 
