234 THE POWER OF RESISTANCE TO EXTREMES 



The death of plants unable to withstand desiccation is directly due to 

 the withdrawal of water consequent upon the formation of ice, and this 

 must be nearly complete at 30 C. Pictet l observed that rotifers capable 

 of withstanding desiccation were entirely killed by a day's exposure to from 

 150 to 1 60 C., but only in part when kept for the same time at 80 to 

 90 C., while at 60 C. all remained living. It is indeed possible that 

 some bacteria are only killed by temperatures of from 100 to 200 C. 

 Whether this is due to the withdrawal of the water of imbibition or not, 

 it is certain that a further fall of temperature may produce death after the 

 whole of the cell-sap has frozen. Bearing in mind also that perfectly dry 

 seeds and spores ultimately die, it may safely be assumed that vitality is 

 not preserved indefinitely long at very low temperatures whether the plant 

 was previously dried or left saturated with water. The experiments with 

 rotifers show indeed that at very low temperatures life may be shortened, 

 and de Candolle found that dry seeds of Lobelia Erinus lost their vitality 

 sooner at very low temperatures than at ordinary ones 2 . 



The fact that many chemical actions cease at very low temperatures 3 

 does not afford any general explanation of the death produced by cold in 

 organisms capable of withstanding desiccation, nor are physiological 

 experiments altogether satisfactory in which the period of exposure is 

 relatively short. Vitality may be maintained for a long time in various 

 conditions of rigor, and that this also applies to cold-rigor is shown by the 

 fact that arctic plants may remain living although frozen for half the 

 year 4 . 



These effects are produced by slow as well as by rapid cooling, and it is 

 the low temperature and not the thawing which produces death. A non- 

 resistant plant is killed by the actual freezing and cannot be saved by the 

 most careful thawing, whereas resistant plants remain living however 

 rapidly they may be thawed. Thus plants of Stellaria media frozen at 

 6 C. remain living when suddenly brought into a warm room, or when 

 thawed by immersal in water at 25 C. Frisch 5 observed that motile 

 bacteria frozen at 59C. immediately began to move when thawed in less 

 than a minute. 



The power of withstanding these rapid changes is of great importance 

 in nature, for the sun's rays may rapidly thaw frozen plants, especially in 



1 Pictet, Archives d. sci. phys. et nat. d. Geneve, 1893, 3 se"r., T. XXX, p. 311. 

 3 Nageli (Sitzungsb. d. Munchener Akad. 1861, I, p. 271) erroneously supposed that a 

 further fall of temperature was without effect when the plant was once frozen stiff. 



3 Pictet, Zeitschr. f. physikal. Chem., 1895, Bd. xvi, p. 417. 



4 According to Charpentier (Bot. Ztg., 1843, p. 13) Trifolium alpinum, T. catspitosum, Geum 

 tnontamtm, and Cerastium latifolium continued to grow after being buried for four years under a 

 glacier. They were not, however, frozen the whole of this time, since during summer the temperature 

 beneath the ice might rise up to or even above zero. 



5 Frisch, Sitzungsb. d. Wiener Akad., 1877, 3- Abth., Bd. LXXV, p. 257. 



