84 SUMMARY OF CURRENT RESEARCHES RELATING TO 



earlier true leaves. The water content of the soil does not appear to* 

 affect the germination percentage to the degree that might have been 

 expected. A single plant of Solarium nigrum may produce over 2000' 

 potentially viable seeds ; in Scrophularia the germination percentage 

 amounted to from 56 to 70 per cent, in the favourable conditions of the 

 laboratory. 



Influence of a very Low Temperature on the Germination of 

 Seeds.* — Sir W. T. Thiselton-Dyer states, as the result of a series of 

 experiments carried on by Prof. G. Dewar and himself, that immersion 

 for upwards of six hours in liquid hydrogen (a temperature of 453° F- 

 below melting ice) appears to produce no injurious effects whatever on 

 their power of germinating. The seeds operated on were those of 

 Brassica alba, Pisum sativum, Cucurbita Pepo, Mimulus moschatus,. 

 Triticum sativum, and Hordeum vulgare. 



Resistance of Seeds to High Temperatures.f — M. V. Jodin states 

 that seeds (peas and cress), when heated at once to 98° C. for 10 hours, 

 are completely killed, but, when heated first to 60° for 24 hours, and 1 

 then to 98° for 10 hours, a certain proportion (30 to 60 per cent.) 

 retain their power of germination. Heated to 40° in sealed tubes for 

 about 20 days, the same seeds entirely lost their power of germination ; 

 but this power was retained if a substance capable of absorbing water, 

 like quick-lime, was introduced into the tubes. 



Ascent of Sap.} — Mr. H. W. Chamberlain gives, in great detail, 

 the results of a long series of experiments, on a variety of plants, on 

 the phenomena connected with the ascending sap. Among the more 

 important are the following : — After decapitation an efflux of water was- 

 detected in some plants, but not in others. Root-pressure was stronger 

 in herbaceous than in woody plants. The period of the year has but 

 little effect on the root-pressure when the plant is in active growth. 

 As regards a daily periodicity, the plants under examination could be 

 divided into three groups: — in the first there was no trace of any daily 

 periodicity in the flow of sap ; in the second there was a daily periodi- 

 city, but the times for the maxima and mimima were uncertain ; in 

 the third group the periodicity was regular and permanent. Variations 

 in temperature (between 5° and 6°) had no considerable influence upon 

 the root-pressure. Moistening of the leaves greatly favours the ascent 

 of sap ; while the saturation of the soil is very unfavourable. Succulent 

 plants are characterised by a replacement of root-pressure by an ener- 

 getic aspiration. The larger and more strongly developed the roots, 

 the stronger is the root-pressure. 



Absorption of Water by Decorticated Stems.s — Mr. G. E. Ripley 

 states, as the result of a series of experiments on different woody plants, 

 that cut stems wither more slowly when decorticated than when entire. 

 The difference in the period before withering varies greatly, but is often 

 very considerable. 



* Pi-oc. Roy. Soc, lxv. (1899) pp. 361-8 ; Ann. of Bot., xiii. (1899) pp. 599-G05. 

 t Comptes Rendus, exxix. (1899) pp. 893-1. 



X Bull. Lab. Bot. Univ. Geneve, ii. (1897) 310 pp., 7 pis. and 3 figs. See Bot. 

 Centralbl , lxxix. (1899) p. 311. § Pioc. Indiana Acad. Set, 1898, pp. 169-74. 



