ZOOLOGY AND BOTANY, MICROSCOPY, ETC. GJ9 
belief) no diminution of the amount of mineral substances in the leaves 
takes place during the autumn. The amount of nitrogen, potassium, and 
phosphorus was found (in the beech) to be practically unchanged up to 
the end of September. This, however, does not negative the theory of 
a passage of mineral substances back from the leaves to the petiole and 
the stem ; but this is counterbalanced by the transpiration-current. 
Functions of Stomates.* * * § — Using the hygroscopic apparatus already 
described for measuring the opening and closing of stomates, Prof. F. 
Darwin says that, notwithstanding previous statements to the contrary, 
partial closure of the stomates of marsh and aquatic plants does take 
place when the leaf is gathered. In many cases closure of the stomate 
is preceded by temporary opening, which may occur almost simul- 
taneously with the gathering of the leaf. In dark stormy weather the 
stomates may be nearly closed by day, even in summer. After darkness 
has been prolonged for several days, the stomates gradually open. The 
great majority of plants (not nyctitropic) show some closure of the 
stomates by night. 
Assimilation of Nitrates in the Dark.f — From experiments made 
by M. U. Suzuki, chiefly on barley, he has come to the conclusion that 
flowering plants can assimilate nitrates in the dark, and form proteids 
from them. The nutrient solution used contained 0*2 per cent, sodium 
nitrate, 0 • 1 per cent, potassium monophosphate, 0 • 1 per cent, potas- 
sium biphosphate, 0 * 1 per cent, magnesium sulphate, 0 • 07 per cent, 
calcium sulphate. 
-• Growth of Roots.j — From observations made on a large variety of 
trees, Herr 0. G. Petersen establishes a general law of seasonal perio- 
dicity in the growth of roots, — active in April and May, and again in 
September, but suspended in J uly. This periodicity was least clearly 
manifested in the maple and the ash. In the oak the autumnal fresh 
formation of roots takes place in October. The growth of the myeorhiza 
continues until November. The annual formation of rings in the main 
roots usually begins in May, and ends in September or October. 
Influence of the surrounding Medium on the Growth of Roots. § — 
Herr J. Wacker states that, as in the case of land-plants ( Vicia Faba , 
Lujoinus albus, Helianthus annuus , Cucurbita Pepo) the growth of the 
primary root almost ceases when they are cultivated in water ; so also 
with water plants ( Lemna minor , L. trisulca , Azolla filiculoides , Hydro - 
charis morsus-ranse) the growth of the primary root almost entirely 
ceases when they are planted in a saturated soil. This is not the result 
of a difference in the proportion of oxygen in the two media. In mud 
the roots of land plants perish either from the absence of free oxygen, 
or from the presence of various products of decomposition. They have, 
apparently, not the same power of absorbing oxygen that those of bog- 
plants possess. 
* Proc. Roy. Soe., Ixiii. (1898) pp. 413-7. Nature, lviii. (1898) pp. 212-3. Cf. 
this Journal, ante , p. 134. f Bot. Centralbl., lxxv. (1898) pp. 289-92. 
X Overs. Kgl. Danske vidensk. selsk. Forhandl., 1898, No. 1 (many figs.). See 
Bot. Centralbl., lxxv. (1898) p. 272. 
§ Jahrb. f. wiss. Bot. (Pfeifer u. Strasburger), xxsii. (1898) pp. 71-116. 
