Atmospherical Influences 65 



The proper treatment for trees whose shoots have been 

 frost-killed, is to head them back severely to sound wood 

 in order to get rid of the injured, and to supplant it by 

 active, healthy growth. This pruning is best done shortly 

 before the fohage starts, when the extent of the injury can 

 be better noticed. Trees or branches thus injured by fall 

 frosts may sometimes leaf out and bloom in spring, but they 

 soon succumb for lack of sufficient water-supply through 

 the injured parts. 



The loss of foliage with the approach of winter, which is 

 a natural physiological process, is more or less connected 

 with changes in temperature conditions, and hence in some 

 years may occur earlier, in others later than usual, without 

 being a sign of sickness. Besides leaves, certain species, 

 like Elm, Linden, Black Locust, Poplar, Willow, Oak, 

 Bald Cypress, and many others shed more or less regularly 

 whole branchlets, from one to ten years old, and more. 

 This phenomenon may also be considered pathological, 

 although it occurs quite frequently, and sometimes regu- 

 larly and systematically. Neither the cause nor the rem- 

 edy is known. This shedding of branchlets is entirely 

 different from the loss of the tips by frost, regularly experi- 

 enced by some species like Linden, Elm, and Sycamore, and 

 by exotics which find the summer too short to finish their 

 growth. This habitual freezing back can be prevented by 

 defoliating the branchlets before growth ceases, when the 

 wood will harden before the frosts come. 



In other species such loss of the young twigs occurs only 

 under special conditions, namely, when the young wood 

 has not been matured in time. This is apt to happen when 

 a late and warm moist fall follows a dry summer, inducing 

 belated growth which does not harden but remains succulent 

 and is nipped more or less severely by the earl}' frosts. 



