EVERGKEEN TREES IN WINTER. 315 



lower temperature affects the plant in diminishing the evaporation 

 of water, it has but little influence in wholly stopping it. 



That the amount of transpiration greatly depends upon the 

 temperature of the soil in which the plant grows, was first clearly 

 shown by the well-known experiment of Sachs'^ He observed 

 that some herbaceous pot- plants, e.g. Cucurbita, Nicotiana, &c., 

 wither when the soil full of moisture was exposed to a temperature 

 of 2-4°C., and he attributed this to the deficiency of the absorption 

 of water. It must, however, not be concluded that, from the 

 above experiments, the absorbing activity of the root of many 

 plants in temperatures near the freezing point, or even below it, 

 is completely destroyed : on the contrary, in several species 

 of plants the root or even the cut-branches can absorb water 

 considerably, as Kosaroff^^ has recently shown. 



The most interesting fact that the diminution of transpira- 

 tion of evergreen trees in winter has a close relation to the 

 closure of the stomata in that season, can be seen from the re- 

 sults of the investigations made by several authors. Stahl, who 

 laid stress especially upon this point, says: "Bei unseren 

 immergrünen Straüchern und Bäumen, deren Existenz ohne 

 den Spaltenschluss gar nicht möglich wäre, tritt derselbe 

 schon frühzeitig im Herbste ein."''^ He has proved this fact by 

 his " Kobaltprobe ""*'; and has shown that in some winter-green 

 trees, for example, Hedera Helix, ten days were required to make 

 the stomata reopen in a hot chamber. 



1) Sachs, Das Erfrieren bei Temperaturen über 0°. Bot. Ztg., Bd. XVIIT, 1860, p. 124. 

 Compare Sachs, Text Book of Botany 1882, 2nd Ed., p. 704. 



2) Kosaroff, Einflu?s verschiedener äusseren Factoren auf die Wasseraufnahme der 

 Pflanzen. Inaug. Disst. Leipzig. 1897. 



3) Stahl, Einige Versuche über Transpiration und Assimilation. But. Ztg., Bd. LXX, 

 1894, p. 126. 



4) 1. c, p. US. 



