64 Diagnosing of Diseases 



as the life functions of a tree are concerned, that the influ- 

 ences of the one may be counteracted or increased by the 

 influence of the other: drouthy conditions of the atmosphere 

 may be met by irrigation at the root; cloudy weather may 

 counteract deficiency of water at the root; a warm soil may 

 start growth so early in the season that frost will do dam- 

 age, which othenvise would have been harmless. These 

 relations involve complications which may baffle even an ex- 

 pert's diagnosis as to the true cause of physiological disease. 



The humidity and temperature of the atmosphere are 

 conditions of moment, especially in frost phenomena, but 

 the soil plays in these no subordinate role. Indeed, many 

 frost phenomena are more dependent on soil conditions than 

 on temperature. Stiff, clayey soils are, as a rule more hable 

 to frost than light soils, and a soil producing over-luxuriant 

 growth is apt to expose the imperfectly ripened wood to 

 damage by early frosts in the fall. 



There are three seasons in which frost may occur with 

 differing effects, namely, the fall or early frosts, the winter 

 cold, and the spring or late frosts. 



The early frosts occurring in the fall at the end of the grow- 

 ing season will be felt especially by those leaves which hsive 

 not been shed, and by the tips of the shoots which have 

 not perfected their growth. Damp locations seem to induce 

 this late growth, or at least do not seem to mature the wood 

 as well, and they are also more liable to fall frosts than drier 

 regions, hence draining may reduce the frost danger. 



In certain positions the danger from frost is greater than 

 in others, and, if this is due to cold air settling in a given 

 place, say a group of trees, it may be corrected b}' opening 

 up the group and thus creating a draft for the cold air to 

 draw off". Conifers may suff'er especially in such "frost 

 holes." 



