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 fmally of entire 

 branches. 



In light sandy soils this deficiency of water at the root 

 may be due to o\er-drainage, or, in compact soils, to the 

 packing and caking of the surface layers, preventing aeration 

 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 temperature occurs and dry winds prevail 

 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 w^ater which do not concern us here. 



Different species make diflerent requirements on water- 

 supply, some adapting themselves to deficiency or excess 



