THE DISEASES OF CONIFERS. 



127 



it must be remembered that wrong conclusions — i.e., wrong 

 diagnoses — lead to impro^Der treatment in plant-diseases, as 

 they do in human diseases. 



The diseases of Conifers are, in fact, like the diseases of other 

 living beings, cases of disturbances in the struggle for existence 

 going on among the structural elements of the tissues, &c. 



My task to-day is confined to the discussion of only two 

 categories of these diseases — those due to fungi, and those due 

 to disturbing actions of the inorganic environment ; * the simplest 

 plan will be to take some of the groups of Conifers seriatim, and 

 toach briefly on their prominent maladies. 



I. The Pines. 



Owing to their very resinous nature, the Pines generally are 

 not so apt to suffer from injuries which result from the exposure 

 of open wounds as are many other trees, and it is astonishing how 

 much knocking about the hardy species will endure ; breakages 

 from wind, heavy snow, the cutting and biting of man and other 

 animals, and so forth, are readily healed over by occlusion t in 

 the case of most of the species. 



A very common cause of disease and death in Pines is the 

 breaking of the ascending water-current from various actions of an 

 unsuitable environment. Speaking generally, the Pines require 

 light, open, and well-drained soils, as deep as possible ; t and 

 many aspects of disease in them are due to the non-fulfilment 

 of these conditions. 



Unquestionably one of the worst of these dangers results 

 from the clogging of the soil at the roots, whether due to wet 

 clay, stagnant water, the covering up or hardening of the surface 

 — e.q., by means of pavements, &c. — or other processes. 



The general course of events is much the same in all these 

 cases. The primary cause of the injury is want of oxygen at the 

 roots, for without due supply of that gas in the water to which 

 the living and absorbing parts of the smallest root-fibrils have 



* Those diseases wliich are due to the injurious action of animals, 

 especially insects, being treated of separately. 



t I suggested this word in 1885 as a translation for the German 

 Ueherwallung, and it has been accepted by my colleagues and others, 



^ "We are not concerned with exceptions to this very general vnle~e.(f., 

 the Austrian Pine and others will grow on shallow and even rocky soils 

 and there is considerable latitude as to what particular Pines will endure. 



