2(^8 



the increase in volume of llic I'rozcii s;ip cannot, in fast 

 thawing, resume their normal size smoothly enough 

 ("avec assez de douceur"), then they break, the sap 

 evaporates and the plant dries up. 



A similar idea is held by Pichel (1816, quoted by Miil- 

 ler-Tliurgau, 1886). Injury in twigs would result from a 

 tearing of vessels or of essential structures in the too 

 rapid thawing of the unequally expanded outer and inner 

 layers of the twigs. The free course of the sap would 

 thus be disturbed. 



Goeppert (1830) called into doubt the view of many 

 of his predecessors that slow thawing saves frozen plants 

 from death. He thawed slowly, at about 0°, in snow^, frozen 

 bulbs of onions, tulips, etc., and observed that they were 

 killed. 



The experiments of Sachs (1860; see also Sachs' Hand- 

 buch der exp. Physiol, der Pflanzen, Leipzig, 1865 and 

 later editions) again revived the older theory that slow 

 thawing can forestall the death of frozen plants. He 

 froze pieces of beet and of pumpkin and leaves of beet, 

 cabbage, bean, etc., at - 4° to - 6°R (- 5° to - 7.5°C) and 

 thawed them in water at 0^, in air at 2' to 3°R or in 

 water at 6° to 10°R. In the first case, wdth slow thawing 

 at 0% the plants were alive, in the last two cases they 

 w^ere killed. Sachs' interpretation is that when thawing 

 is slow the molecules of water pulled loose from the pro- 

 t()l)lasm during crystallization can again take up their 

 former position and reestablish the conditions existing 

 before freezing, while if thawing is rapid some of the 

 water may flow away and not be reabsorbed and thus the 

 previous conditions of concentration and imbibition can- 

 not be restored and death may result. As to the fact that 

 a lower water content decreases the sensitivity to cold, 

 Sachs explains it by assuming that when there is less 

 water to freeze it can more readily be reabsorbed after 

 thawinij;. 



