ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
217 
resistance to the electric current, spores not being killed in the course 
of an hour ; while Bacillus subtilis and vulgaris showed a much greater 
sensitiveness. It is, however, not proved that this is universally the 
case with bacteria. 
Relation of Nutrient Salts to Turgor.* * * § — Mr. E. B. Copeland has 
experimented on the effect on the growth of plants of various solutions 
of mineral salts ; the plants employed being Phaseolus vulgaris , Pisum 
sativum , Sinapis alba , Polygonum Fagopyrum, Zea Mays. He finds that 
potassium presented to the roots of plants causes the cells of both root 
and stem to exhibit a higher turgor than they can do when it is replaced 
by sodium. Potassium is therefore a factor, direct or indirect, in the 
turgor of the plant ; and there is no experimental ground for attaching 
this significance to any other constituent of the mineral food. From 
the analysis of the sap the author further concludes that the influence 
of potassium on the turgor of the plant is direct. 
Influence of Low Temperatures on the G-erminative Power of 
Seeds.j* — Mr. H. T. Brown and Mr. F. Escombe have subjected a 
number of air-dried seeds (containing from 10 to 12 per cent, of natural 
moisture), belonging to different natural orders — Graminese, Cucur- 
bitaceae, Leguminosae, Geraniaceas, Compositae, Umbelliferas, Convol- 
vulaceae, Liliaceae — for 110 consecutive hours to a temperature of from 
— 183° to —192° C., subsequently thawing them very slowly. Their 
germinative power showed no appreciable deterioration ; the resulting 
plants grew to full maturity, and were healthy. Of the seeds some 
contained endosperm, others did not ; the reserve-material consisted in 
some cases cf starch, in others of oil or mucilage. 
Periodicity of Rool-Pressure.t — From the facts recorded on this 
subject, Mr. M. B. Thomas concludes that the measure of the root- 
pressure is the osmotic activity of the root-hairs, due to the presence in 
them of organic acids and other substances which show a great affinity 
for water. The root-pressure does not seem to have any relation to the 
previous periodicities of the vital activities of the plant. The author 
believes the periodicity of root-pressure to be inherent in the plant, and 
to have been acquired either by previous adaptation to environment or 
as the result of the action of some constant or periodic changes in the 
plant. 
Aeration of the Trunks of Trees.§ — As the result of a series of 
experiments on a large number of different kinds of forest-trees, M. H. 
Devaux finds that the permeation of the air into the interior of the stem 
is effected mainly through the agency of the lenticels, which are for 
the most part open, even in the main trunk. He finds, moreover, that 
the crustaceous lichens which frequently cover the trunks of trees do 
not sensibly prevent the access of air to the lenticels or impede the 
exchange of gases which takes place through them. 
* Bot. Gazette, xxiv. (1897) pp. 399-416. 
t Proc. Boy. Soc., lxii. (1897) pp. 160-5. Nature, Ixii. (1897) pp. 138-9,! 150. 
Cf. this Journal, ante , p. 102. 
a ; X Proc. Indiana Acad. Sci., 1896, pp. 143-7. 
§ Comptes Rendus, cxxv. (1897) pp. 979-82. 
