378 Ewart. — The Action of Cotd and of 
effect upon the chloroplastids and also upon the cell-plasma, 
and which are least useful in C (^-assimilation 1 . 
The plants which compose a snow-flora must be able to 
withstand sudden and marked extremes of temperature. 
They must be able to have all or almost all of the water 
which they contain removed or converted into solid form 
without being killed, and must be capable of an almost 
immediate resumption of both respiration and assimilation 
when the water is restored, either directly when the plant 
is dry or by thawing when it is frozen. If any prolonged 
latent period of recovery always followed as a necessary 
consequence after short but severe exposure, the plant would 
waste most of the precious day-time exposure in recovering 
and preparing for the full resumption of all its vital activities 
when returned to more favourable conditions. It has already 
been shown that exceedingly resistant plants do actually 
exist, which even after prolonged air drying or exposure 
to severe cold remain living, and almost instantaneously 
recommence to assimilate and respire, when the temperature 
is raised to the optimum, and the normal water percentage 
restored 2 . 
Lagerheim found that the flora of the perpetual snow 
region of Pichincha was composed of four species of Chlamy- 
domonas (Volvocineae), Gloeocapsa , Nos toe, Navicida , Gloco- 
cystis , Rhaphidonema nivale (Ulothrix form), and also a sapro- 
phytic fungus, Selenotila nivalis , in all twenty-one species. 
In Vallidal, Swedish Lapland, Wittrock found about nine 
species of Desmids. Altogether the known snow-flora com- 
prises about seventy species 3 . Wittrock (1. c., pp. 86, 120 ) finds 
that the zygospores of the snow Volvocineae ( Chlamydomonas ) 
and also the resting-stages (non-motile vegetative condition) 
can withstand air drying. The same has been shown to be 
1 Ann. of Eot. Vol. xi, 1897, Sept., p. 477* 
2 Assim. Inhib., 1 . c., pp. 385, 389. (Mosses, Lichens, Protophyta.) 
3 Lagerheim, Die Schneeflora des Pichincha, Ber. d. Bot. Gesell., 1892, Bd. x, 
p. 517 ; V. B. Wittrock, Om Snons och isens flora, sarskeldt i. de arktiska traktema. 
Stockholm, 1883. 
