ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
541 
L can, therefore, never exceed unity, and may be reduced to zero. On 
the whole, direct sunlight exercises comparatively little influence on the 
growth of plants ; diffused daylight is the most favourable condition. 
The lower the temperature, the larger is the amount of light required 
by the plant. There are comparatively few plants that receive light 
equally in all directions. In forests the trees receive it almost entirely 
from above ; plants growing against a wall or rock only from one side ; 
plants growing by water-side often by reflected light from below. The 
average light-requirement of a plant decreases with age. In a forest 
the light-requirement of the undergrowth must be less than that of the 
trees. The loss of leaves in the winter is of advantage only in those 
climates where the intensity of the light is small at the time when the 
leaves unfold. Hence in the tropics most trees are evergreen. 
Gain and Loss of Leaves.* * * § — As the result of a series of experiments 
on Helianthis, Mr. S. Thompson and Mr. W. W. Prendergast estimate 
the average loss in dry weight of the leaves during the night, between 
July 21st and August 1st, at 1*41 grm. per sq. metre ; the average gain 
during the day-time, between July 27th and August 8th, at 1*9 grm. 
per sq. metre. The average gain in weight of unshaded was, in the 
majority of cases, greater than that of shaded samples. 
Latent Life of Seeds. f — M. V. Jcdin states, as the result of experi- 
ments, that peas will retain their j^ower of germinating longer if kept 
in vapour of mercury, where there is no possibility of their respiring, 
than if exposed to the action of oxygen, even when they do not gain in 
weight. In the latter case the cause of the loss of the power of ger- 
mination is no doubt a modification of the intramolecular reactions of 
protoplasmic substances. 
Antidromy.f — Mr. G. Macloskie gives several instances of this 
mode of growth in Flowering Plants and in Vascular Cryptogams. It is 
not uncommon for an'tidromic individuals to spring from the same root- 
stock. 
Paratenic Trophism.§ — From experiments made on the fir (Pinus), 
Prof. J. Wiesner concludes that unequal growth in thickness shows 
clearly the influence on growth of the position of the branches in respect 
to the horizon — e. g. in the stronger growth of the under side ( hypo- 
trophy) . This hypotrophy of a horizontal stem may be continued in 
the vertical portion, where it passes over into a gradually diminishing 
hypertrophy. 
Ascent of SapJJ — Prof. E. Askenasy describes an apparatus by means 
of which he is able to make water ascend in tubes above the barometric 
level, and thus to prove the truth of his theory that the main factor in 
the ascent of sap in plants is the imbibing power of the cell- walls of the 
leaves. 
* Minnesota Bot. Studies, 1896, pp. 575-8. 
t Comptes liendus, cxxii. (1896) pp. 1319-51. Cf. this Journal, 1S95, p. 655. 
x Bull. Torrey Bot. Club, xxiii. (1896) pp. 202-5. Cf. this Journal, ante, p. 204. 
§ Ber. Deutsch. L’ot. Gesell., xiv. (1896) pp. 180-5 (1 fig.). Cf. this Journal, 
ante, p. 326. 
|| Verhandl. naturhist.-med. Yer. Heidelberg, v. (1896) 20 pp. Bee Bot. Ccn- 
tralbl., lxvi. (1S96) p. 379. Cf. this Journal, 1895, p. 550. 
