339 



xV tletailod s;tiuly of the relation of low teniporatiiros to the growing: 

 of wheat has been made by S. G. Wright, of Indiana, from which I 

 take the following conclusions : 



SIcef. — When the winter wheat has its blades covered with ice that 

 has fallen as sleet, and after the ice has melted otf a microscopic exam- 

 ination shows the cellular structure to be altered, the epidermis is 

 separated from the underlying cells and there is a general disunion of 

 tiie cells, and when the growing season comes the plants are found to 

 be entirely dead. 



Sudden thawing. — '\Mieat plants exposed to a very low freezing 

 temperature in dry air if thawed out slowly are not much injured, 

 but if thawed out rapidly the younger sprouts are completely killed 

 and the older ones subsequently die. The similar rule obtains for the 

 germination of seeds. ^^Tien frozen seeds were quickly thawed out 

 only 18 per cent germinated, but when slowly thawed out 86 per cent 

 germinated. 



Freezing temperature of the juices of the ivheat. — The juice ex- 

 tracted by pressure from the wheat has a lower freezing point than 

 that of pure '\\'ater when contained in its original living tissues, but 

 after being extracted by pressure it freezes at an intermediate point 

 below that of pure water. Again, the juice extracted from plants 

 that have been exposed to a low winter temperature withstands freez- 

 ing better than the juice from plants that have not had such exposure. 

 For example, the juice within the cells was not frozen at — 13° C, 

 while that thrust out of the cells froze at — 6° C., and in general the 

 power to resist freezing is increased by exposing plants to the ordinary 

 winter temperatures of the open air. 



Method of sowing. — The best method of sowing wheat in order 

 that it may withstand severe winter weather is (1) to avoid mulching 

 or having any layer of porous material about the roots of the wheat, 

 as experiment shows that this is a decided injury both to the winter- 

 ing, the after growth, and the harvest. An average depth of seed 

 jolanting of 1.5 inches is much better than three-fourths inch or 3 

 inches. 



Range of temperature for germination. — According to Sachs, the 

 minimum temperature is 5° C. and the maximum 37° or 38° C. 

 According to Haberlandt, the temperature for germination ranges 

 between 0° and —4.8° C. at the lower limit and 31° to 37° C. at the 

 upper limit. Wright's experiments, at a constant temperature of 

 39° C, gave germination successful in forty-eight hours; at a tem- 

 perature of 42.5° C. only a very few seeds could be made to germinate. 

 At a temperature of 0° C. the seeds germinated in ten days ; hence the 

 extreme range of germinating temperatures for winter wheat of the 

 varieties thus tested in Indiana is from 0° to 42.5° C. As to the effect 



