46 DISEASES OF TREES 



are formed under the protection of the epidermis of the host- 

 plant, which is ruptured only after the spores have ripened. 



The fact that in summer, in spite of a more favourable 

 temperature, far fewer so-called " Toad-stools " spring from the 

 ground than in October, when the atmosphere is relatively much 

 more humid, shows clearly how dependent on a constant supply 

 of moisture in the air is the development of sporophores that 

 expand entirely outside the substratum.* The extensive 

 distribution which the larch-fungus, Peziza Willkommii, has 

 experienced in the plains of Germany is almost entirely due to 

 the abundant production of fructifications and spores which have 

 ripened perfectly in the moist, stagnant air of the dense low- 

 lying woods ; whereas in the breezy Alps the fructifications 

 almost always wither before they have had time to mature. 



Not only does a moist atmosphere affect the ripening of the 

 fructifications and the germination of the spores outside the 

 plant, but it also appears to have great influence on the develop- 

 ment of the fungus even inside the plant. This assumption is at 

 least supported by the fact that Cceoma pinitorqinnn, which is a 

 perennial in the shoots of the pine, assumes the proportions of a 

 plague when the month of June is wet, but causes scarcely any 

 appreciable damage when the weather is dry. 



As regards their adaptations for nutrition, fungi may be 

 arranged in two great divisions. Parasite is the term applied 

 to those fungi which draw their nourishment from living 

 organisms ; saprophyte, to those which live on dead bodies. It 

 is not possible, however, to draw a sharp line of demarcation 

 between these two categories. To begin with, it may often 

 be disputed whether an organic body is to be called dead 

 or living. By far the greater part of the wood of trees is made 

 up of dead cells, the walls of which alone remain ; and only 

 a relatively small part, consisting of the parenchymatous cells 

 of the wood and medullary rays, remains alive and contains 

 protoplasm. Seeing that many fungi live only on the old 

 stumps of trees and on trees that have long been felled or 

 otherwise killed, whereas others destroy growing trees, it would 



* [The whole subject needs thorough investigation, however, and it would 

 be particularly valuable to have more information as to the importance of 

 sunlight and other factors in this connection. ED.] 



