374 Ewart . — The Action of Cold and of 
substrata. It therefore embraces Pleurococcus , Scencdesmns , 
Protococcus and allied forms, Schizophytes such as the 
Cyanophyceae and Bacteria, and such plants as Vaucheria , 
Mucor , &c. It is in this group that the forms most resistant 
to cold are met with, though all grades of resistant powers 
are shown. In this connexion it is important to notice 
the relationship which exists between resistance to desic- 
cation and resistance to freezing. All plants or parts 
of plants which can withstand desiccation can also with- 
stand freezing 1 , though many plants which can be frozen 
and yet remain living cannot be fully desiccated or even 
completely air-dried without being killed. Thus Schroder 2 
found that the leaves of Echeveria secunda began to die on 
losing from 50 to 60 per cent, of the water normally 
present, and died on losing 60 to 80 per cent. Sedum 
elegans gave similar results, but was able to withstand more 
complete desiccation. These plants and Semper vivum also 
can, however, survive exposure even to comparatively severe 
cold 3 . The reason for this difference appears to be that 
freezing involves a less complete and perfect withdrawal of 
water from the living cell and cell-plasma than desiccation 
does, and that on thawing the water is immediately available 
for reabsorption, whereas in desiccated specimens it is removed 
not merely from the cell, but away from the plant entirely. 
It is with regard to the capillary imbibed water that the 
difference between freezing and desiccation is probably 
especially manifest. By complete desiccation, not only all 
free water, but also very nearly the whole of the capillary im- 
bibed water, may be removed ; and only certain seeds, Mosses, 
Bacteria, &c., can withstand desiccation reducing the amount 
of water present to as low as from 1 to 2 per cent. When 
a moist plant is frozen, however, the capillary imbibed water 
1 See Assim. Inhib., Journ. Linn. Soc. Bot., Vol. xxxi, 1896, pp. 374-402 ; and 
Power of withstanding Desiccation in Plants, Trans. Liverpool Biol. Soc., Vol. xi, 
1897, p. 151. 
2 Bot. Unters. Tubingen, Bd. ii, Heft 1, 1886, p. 5. 
3 See Assim. Inhib., 1896, 1. c., p. 389. 
