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at the beginning- of freezing at near-zero temperatures; 

 2. A further withdrawal of water at lower temperatures 

 causes death, o. Cold resistance is increased by dehydra- 

 tion (wilted tobacco leaves were found to resist freezing 

 more than fresh ones) ; 4. The high concentrations which 

 result from delwdration exert a toxic effect ; 5. The differ- 

 ences in resistance to both freezing and drying in various 

 plants are specific characters. Molisch furthermore at- 

 tributes the resistance of bacteria, spores, seeds, moss, 

 etc., to the fact that these organisms can be exposed to 

 low temperatures without releasing their water. 



According to Matruchot and Molliard (1902), who had 

 observed that, in frozen plant cells, Avater had been sep- 

 arated from the cytoplasm and from the nucleus, the de- 

 hydration theory explains niosl: of the facts known on 

 the action of low temperature. They discuss, in partic- 

 ular, the following ones : 1. Cytoplasmic streaming de- 

 creases and finally stops, when a cell is cooled; this 

 would be due to the more solid consistency acquired by 

 protoplasm on the withdrawal of water. 2. Numerous 

 plants and animals revive after freezing or after dry- 

 ing when water is supplied to them; in both cases, the 

 organism would come back to life if water could be re- 

 imbibed by the protoplasm and the conditions which 

 existed previously reestablished, while the organisms 

 would die if the separation of water went so far as to 

 constitute an irreversible process. 3. The injurious ef- 

 fect of too rapid thawing would be due to the sudden 

 invasion of the dehydrated tissues by water, a too rapid 

 imbibition rendering impossible the reestablishment of 

 the previous state. 4. The various degrees of resistance 

 oiTered by different species to both desiccation and freez- 

 ing would be explainable by different specific water-hold- 

 ing capacities. 5. The high resistance to cold of plants 

 with a thick or heavily cutinized epidermis could be at- 

 tributed to the ability of these plants to retain water. 



