43 



ents. In these orchards we have had opportunity to observe the 

 results following cold periods that killed all the buds, cold periods 

 that killed nearly all of them, and cold periods that left a fair crop, 

 but in no case has there been any apparent effect on hardiness re- 

 sulting from the use of potassium as a fertilizer. Twigs were se- 

 cured from these plots in winter, spring, and summer and the density 

 of the sap of the cortex determined by expressing the sap, and deter- 

 mining its freezing point, and no difference in the density could be 

 detected between the plots fertilized with potassium and those re- 

 ceiving no fertilizer. These determinations could not be made with 

 sap from buds because it could not be secured in sufficient quantities. 



If it were possible to increase the sap density by accumulation 

 in the cell of potassium or other materials applied to the soil, it could 

 possibly affect the killing temperature of the bloom or young fruits or 

 young growth in spring, even if it should have no effect on the killing 

 temperature of the buds in their dormant condition. C. Dussere 1 

 observed apparently a slightly greater hardiness of young grape 

 shoots on vines that had been fertilized with potassium than on vines 

 that were not so fertilized. However, analyses failed to show the 

 presence of more potassium in the wood of those vines receiving 

 potassium fertilizer than in the wood of those that had not received 

 fertilizer. 



It may be said that on our peach plots we have had occasion 

 to observe the effect of spring frosts on the bloom, as well as the 

 effect of winter cold on the buds and have failed to observe any dif- 

 ference due to application of potassium to the soil. 



Briefly summerizing all our results with the relation of sap den- 

 sity to hardiness, we are safe in concluding that, at least in case of 

 plants not in a resting condition, a large amount of dissolved material 

 either in the sap within the cell or in a solution surrounding the cell, 

 will protect the cell from injury due to low temperature, to some ex- 

 tent at least. The protection where plants take the material into 

 the cell seems to be much less than where the material in solution 

 surrounds the cell, if the work of Maximow is confirmed. 



The practical means of increasing hardiness seem to be very 

 limited. Withholding water from plants in a plant bed will check 

 the growth and thus increase the sap density and the hardiness. It 

 was thought possible that with such plants as cabbage which take up 

 potassium salts readily, watering in the plant bed with a solution 

 of such salts would tend to increase their hardiness. However, cab- 

 bage and tobacco plants growing in a hotbed soil watered for eighteen 



>Bul. Soc. Scl. Nat. 5, ser 48 (1912) No. 176, pp. 393. (Bibl. No. 31). 



