6o Diagnosing of Diseases 
from the foliage, the newly formed rootlets dying in the 
dry soil. This results in premature yellowing of leaves on 
single branches, a shortening of the year’s shoot and the 
drying out first of portions of the bark and finally of entire 
branches. 
In light sandy soils this deficiency of water at the root 
may be due to over-drainage, or, in compact soils, to the 
packing and caking of the surface layers, preventing aération 
as well as the penetration of water. This hindrance to 
penetration, especially in paved and asphalted streets, grows 
more and more pronounced from year to year, and hence 
premature loss of vigor is the consequence unless assistance 
is given at the root. 
Since trees get their water-supply from great depths, the 
drouth must be very protracted before the effect is felt, 
except in shallow soils, on rocky ledges, etc. Yet, in our 
country, there occur seasons, when the drouth is so severe 
and protracted that even well-established specimens of 
native trees, such as Rock Maple, and White Pine, have 
their leaves badly scorched. ‘The leaves then do not fall, but 
become brown and dry, and remain hanging on the twigs. 
A very similar appearance of foliage in early spring, espe- 
cially in conifers and other evergreens, such as Rhodo- 
dendrons and Buxus, is due to winter drouth. This is 
experienced usually when, with the ground still frozen, a 
sudden rise of temperatre occurs and dry winds preveil 
which overtax the transpiration current from the leaves. 
This “burning” of the leaves is chiefly confined to that 
side of the tree which is exposed to the prevailing winds. 
In fruit trees there are quite a number of other symptoms 
due to deficiency of water which do not concern us here. 
Different species make different requirements on water- 
supply, some adapting themselves to deficiency or excess 
