R. Newton 3 



1000 atmospheres, and notes that by the apphcation of increasinp; 

 pressure the sohdification point of water can be lowered indefinitely. 

 In buds with small cells, dense tissues and meagre water content. 

 Wiegand (49) found no ice at — 18° C, though in most buds it was present 

 in large quantity. He concluded that the degree of cold necessary to 

 cause the separation of ice is proportional to the force which holds the 

 water in the tissues. Lewis and Tuttle(25) reported that Hving leaves of 

 Pi/rola wrapped around the bulb of a mercury thermometer undercooled 

 to ~ 32-l° C. before ice formation took place. On the other liand, it 

 has been a universal observation since the time of Goeppert(]3) that ice 

 may form in the tissues without injury to hardy plants, so that under- 

 cooling is not of itself a sufficient explanation of hardiness. 



The water content of tissues is related to structure, and it has been 

 shown by several investigators (2, 4, 24, 37, in, 13, 14) that dry matter con- 

 tent is directly correlated with hardiness. 8inz (44) and Beach and Allen ( 1 ) 

 noted also the importance of structures resisting desiccation, while 

 Pantanelli(35) found injury from frost to be always proportionate to 

 loss of water from the tissues, even when freezing was done in a saturated 

 atmosphere. 



Between the concentration of the cell sap and winter hardiness, 

 Ohlweiler (34) and Chandler (6) found a direct relationship; Salmon and 

 Fleming (39), working with winter cereals, found none. Pantanel]i(35) 

 partly reconciled the conflicting evidence by reporting a relationship 

 in some crops and none in others, including wheat. Probably the sap 

 of all plants increases in concentration during the hardening process, 

 but not necessarily in proportion to the degree of hardiness attained. 

 However, the earlier evidence as to the importance of the accumulation 

 in the sap of substances of a protective nature, especially sugars, has 

 received further support. Gassner and Grimme(i2) and Akerman and 

 Johansson (2) reported that hardy varieties of \vinter wheat and other 

 grains were richer in sugar, the differences between varieties corre- 

 sponding to differences in degree of hardiness. Pantanelli (35) found that 

 sugar was rapidly used up during exposure to low temperatures, and 

 that hardiness was related to the quantity of sugar retained by the plant. 

 The association of sugar accumulation with hardening by cold has been 

 pointed out again by Rosa (37) and Coville(7). 



On the other hand, Harvey (Hi) found that cabbages acquired hardi- 

 ness on five days' exposure to + 3° C, before any great change occurred 

 in the carbohydrate equihbrium. He beHeves the principal effect of the 

 hardening process to be a change in the constituents of the protoplasm, 



1—2 



