110 RECORD OF CURRENT RESEARCHES RELATING TO 



apparent between the young plants from the frozen and unfrozen seeds. 

 In the case of the fourth species, however — the wheat — seven only 

 germinated, which is accounted for by the fact that alcohol, poured 

 into the test-tube to keep the thermometer free from ice, had got into 

 the tube containing these seeds, and spoilt them. 



A second experiment was made a few days later with thirteen 

 species, the seeds of which were placed along with fragments of metal 

 in a single hermetically sealed tube, and this again in a test-tube as 

 before. When — 40° C. was reached, liquid protoxide of nitrogen was 

 poured into the test-tube, and the refrigeration continued for two 

 hours, till —80° C. was reached. No precaution was taken to 

 graduate the return of the seeds to the surrounding temperature. 

 The next day they were sown as before. All germinated and 

 produced perfectly normal plants, with the exception of three species 

 which were evidently of a bad stock, as both frozen and unfrozen ones 

 remained sterile. 



None of the seeds experimented on had been specially dried ; they 

 were gathered in 1877, with one exception — Mimosa pudica — the 

 seeds of which were fifteen years old. 



It is proposed to continue these investigations, and to extend them 

 to a greater variety of germs, animal as well as vegetable, submitting 

 both to still longer and more severe tests. 



Influence of Light on the Penetration of the Soil by the Roots of 

 Seedlings.* — The following results have been obtained by Dr. K. 

 Eichter : — When seeds germinate lying on the surface of the soil, 

 the roots will only penetrate the soil under certain conditions ; the 

 following being the most important : — 



1. The temperature must be at a certain minimum elevation above 

 the zero for the germination of the particular species. 



2. This minimum is much lower for the same species when the 

 seeds are exposed to the light than when placed in the dark. The 

 reason of this phenomenon is that, under the influence of light, a 

 transformation takes place of light into heat, as can be shown by 

 culture experiments at temperatures above the most favourable for the 

 germination of the particular species. 



3. A pressure of the roots on the soil, whether by the formation 

 of root-hairs or by pressure from without, favours the penetration of the 

 roots. 



4. The influence of the nature of the soil on the power of 

 penetration is limited to the mechanical resistance offered by the 

 former. 



5. Geotropism is necessarily a powerful factor in the power of 

 roots to penetrate the soil. Light influences it by favouring growth 

 by the creation of heat, and hence increasing the geotropic downward 

 curvature. Negative heliotropism, on the contrary, notwithstanding 

 what might have been expected, has no influence on the penetration 

 of roots exposed to light. 



* ' SB. K. Akad. Wiss. (Wien),' June 19, 1879 ; see ' Bot. Zeit.,' xxxvii. (1879) 

 p. 613. 



