EFFECT OF THE FROSTS OF 1908-9 ON VEGETATION. 403 



No doubt the immunity enjoyed by bulbous and most herbaceous 

 plants was due to the short duration of the frost and the little depth to 

 which the earth became really frozen. [At Wisley the earth-thermo- 

 meter at one foot deep did not register lower than 33.9° during the 

 whole winter.] Probably, too, the covering of snow, which was very 

 general, was of some preservative value to the herbaceous plants, 

 though, so far as actual cold goes, it is doubtful whether it is of much 

 assistance, for the grass thermometer at Wisley, covered with snow, 

 registered zero on December 30. Kjellman"^ has shown that snow affords 

 but slight protection against cold itself, but on the other hand its protec- 

 tive power against sudden changes of temperature and against loss of 

 water by transpiration is great. Coverings of straw, etc., act in the same 

 way, and it is interesting, too, to notice that practically all the structures 

 of plants to which protective powers against cold have been ascribed are 

 really devices for checking loss of water, and further, that we cannot 

 recognize in any of those two hundred or so plants which are able to 

 withstand the rigours of the winter at Yakutsk and Verkhoyansk, where 

 the temperature sometimes falls to —60° 0., any structural protective 

 devices at all. 



The question of the cause of death through frost is a very interesting 

 one, a very difficult one, and one that has been the subject of much 

 speculation. Dr. Lindley gave a very full account of the state of know- 

 ledge upon this point in the report already referred to,f but the best 

 recent review of the subject is that of Professor F. F. Blackman in the 

 New Phytologist, vol. iii. Nos. 9 and 10, pp. 354-362. 



We can here give only a brief abstract of this excellent review and 

 refer those interested to it and to the original papers upon which it is 

 based for details. ' m 



It has long been held that the fatal disorganization of the proto- 

 plasm takes place on thawing, and that if thawmg proceeds slowly a 

 plant will recover from exposure to cold which would otherwise have 

 proved fatal. This Molisch has ingeniously disproved and has shown 

 that onl}^ in exceptional instances does the rate of thawing " make any 

 difference to the question of death or recovery. ' ' 



The disorganization of the protoplasm may be due to the withdrawal 

 of water into the intercellular spaces where it freezes^ and the generally 

 accepted theory until recently was that this drying-up of the protoplasm 

 was the direct cause of death; but in 1905 -Mez suggested, and gave 

 reasons for his theory, that for every mass of protoplasm there was a 

 fatal minimum temperature, and in 1906 Gorke brought to light an 

 entirely new factor. He found that as the water is withdrawn from the 

 cells on freezing, the soluble salts become more concentrated and act 

 upon the soluble proteids of the cell, causing them to become in- 

 soluble. He showed that the temperature required to bring about the 

 precipitation of the soluble proteids of plants which suffered easily 

 from cold was much higher than in the case of very resistant plants, 



* Aus dem Lehen der Polarpflanzen. 



t Trans. Bort. Soc. of London, vol. ii. p. 299. 



