2/4 LECTURE XIII. 



water at o C, they survived : even the very sensitive leaves of the 

 Tobacco were not killed by freezing when they were slowly thawed. 



A good illustration of this is afforded by Tautphoeus' experiments 

 with seeds. He exposed the seeds for a night to a temperature of - 5C, 

 and, after either slow or quick thawing, sowed them. The percentage of 

 the seeds which germinated in the two cases is given in the following 

 table : 



1. After slow thawing : 



Not frozen. Frozen. 



Wheat loo 86 germinated. 



Rye 97 88 



Rape 100 97 



2. After rapid thawing : 



Not frozen. Frozen. 



Wheat 100 18 germinated. 



Rye 97 35 



Rape 100 66*5 



The greater tolerance of cold which is exhibited by organs 

 which contain little as compared with those which contain 

 much water, is to be attributed to various causes. In the first 

 place, organs which contain a relatively large quantity of 

 water are in a more actively living condition than those which 

 contain but little; the protoplasm is, in the former case, more 

 susceptible than in the latter to the injurious effect of that 

 disturbance of the equilibrium of the cells which we have 

 spoken of as the result of the freezing of the water which is 

 present in them. Secondly, the cell-sap in relatively dry 

 organs is more concentrated than that of watery organs ; as 

 a consequence the formation of ice involves a lower tempera- 

 ture in the former case than in the latter, and the resulting 

 disturbance is less considerable in the one case than in the 

 other. 



Miiller-Thurgau gives the following illustrations of the difference in 

 the freezing-point for various organs. The succulent labellum of Phajus 

 freezes at - o'56 C. ; the succulent leaf of Sempervivum at - 07 ; the 

 Potato-tuber at -i; the leaf of Tradescantia mexicana at -n6; the 

 Ivy-leaf at - i'5 ; the leaves of Pinus austriaca at -3*5 ; young shoots 

 of Thujopsis at - 4 C. 



