Of pai-ticular interest ai'e the i)lauts reported to die at 

 temperatures above zero. Molisch (1897), among others, 

 investigated their behavior. We refer the reader to tliis 

 aiillior's cliarts for details eoneeriiiiig tlie comparative 

 cold sensitivity of these phiuts. Most of them are from 

 tro])ieal countries and adajitation is tliouglit to play a 

 role in inducing sensitivity. As to the mechanism of death 

 by chilling, the commonly accepted view is that of a dis- 

 turbed balance between the various metabolic functions, 

 mostly trans])iration and al)soi-])tion of water by tlie 

 roots, the temperature coet!icient of these functions being 

 different. 



Another group of higher plants of special interest for 

 their cold resistance is that of some conifers. The trees 

 of the Siberian forests {Larix sibirica in particular) are 

 often mentioned in the literature as typical in that re- 

 spect. Xot only do they withstand exposures of several 

 months to -30° or -40°, but they thrive in climates in 

 which such low temperatures are not uncommon. This re- 

 sistance can evidently not be attributed to any insulating- 

 layer, there is no known substance which would possess 

 the low heat conductivity required to protect the cambium 

 of these plants against the external temperature for that 

 length of time. Such cold hardiness is generally ascribed 

 to the nature of the colloidal cell contents and to the ability 

 of the protoplasm to undergo seasonal clianges in its com- 

 position and concentration. But the fundamental mecha- 

 nism of this phenomenon is still little known. 



Summary: 1. Most of the fungi and algae are killed 

 when exposed to temperatures of - 10° to - 15°. 2. It 

 seems definitely established, however, that some fungi, in 

 tlie actively growing stage, can withstand the tempera- 

 tures of the li(piid gases, although they sliow less resis- 

 tance than the monocellulars to these temperatures. 3. 

 The algae which, like the Hormidimn, are more closely 

 related to the monocellular forms, also resist very low 

 temperatures. 4. The large majority of the higher plants 



