76 Diseases of Truck Crops 



deposited on the outside. Equal injury results 

 when the exterior of the plaxit is at or below the 

 freezing point, and frost is deposited on the plant. 

 It is supposed that in this case the cold does not 

 freeze the water in the cells, but draws it out. The 

 more sap a plant has, the faster it is withdrawn. 

 In this case, then, the plant dies not from cold 

 but from drought. 



Frost conditions are determined by various fac- 

 tors. Trucking lands situated near large bodies of 

 water generally enjoy immunity from frost not found 

 in inland localities. Tender crops growing on low 

 hills or on greatly sloping hillsides, somewhat above 

 the valley floor, are also well protected from frost. 

 Lowlands, particularly those which have no outlet 

 through which the cold air may drain oflf, are not 

 suited for early trucking because of the danger from 

 frost. Lands which are properly drained and cul- 

 tivated win not only produce larger yields, but will 

 also be protected from frost. 



How to Predict Frost. There are usually several 

 signs which the trucker may use as a warning of the 

 approach of frost. Frost should be looked for after 

 unusual warm spells in the spring. The state of the 

 sky is also an indication. Frost is not likely to occur 

 when the sky is overcast because the heat given off 

 by the earth at night does not easily penetrate the 

 clouds and is therefore retained in the air below. 

 On the other hand, during clear nights, the earth's 

 heat readily escapes and this is likely to result in a 

 disastrous drop of temperattire. Frost is brought 



