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 otherwise would have been harmless. These 
relations invol\e 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 réle. Indeed, many 
frost phenomena are more dependent on soil conditions than 
on temperature. Stiff, clayey souls are, as a rule more liable 
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 
ditfering 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 have 
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 by opening 
up the group and thus creating a draft for the cold air to 
draw off. Conifers may suffer especially in such “frost 
holes.”’ 
