INJURIES INDUCED BY PLANTS 91 



it dries up even so early as the beginning of summer. When 

 the part of the tree that is attached is thin, the wood also dries 

 up, and the top of the tree dies and becomes yellow and 

 withered. Very frequently one meets with such withered tops 

 in young spruce woods without being able to find a trace of the 

 perithecia, which only attain maturity when the cortex in which 

 the mycelium is hidden is constantly kept moist. When this 

 occurs as often happens on the lower parts of the stem, where 

 the cortex is kept moist by the shade and protection of the 

 branches a large number of white and yellow cushion-like 

 stromata develop on the dead tissues. These, which are about the 

 size of pin-heads, break through the outer cortical and periderm 

 layers, or remain hidden amongst the loose bark scales. These 

 cushion-like stromata first of all produce large numbers of gonidia, 

 but later on numerous red melon-shaped perithecia are formed, 

 whose ascospores are usually disseminated in winter or spring, 

 when they find their way to the injuries caused by G. pactolana, 

 or to other wounds. 



With the disappearance of the moth as, for instance, in con- 

 sequence of the severe winter 1 879 80, in which the caterpillars 

 were, for the most part, frozen the injury due to this Nectria is 

 of course also diminished, because it has fewer opportunities for 

 infection. Spruces which are attacked only by the moth and not 

 by the fungus hardly ever perish, but after being crippled for a 

 few years recover completely. Spruces which are attacked by 

 Nectria only on one side may also recover, because in the course 

 of time a callus forms over the injured part. The damage, how- 

 ever, which is done to young spruce woods by the trees dying at 

 the top is so great that it seems advisable to limit the spread of 

 the parasite by cutting off and burning all such tree-tops as 

 are attacked by the fungus. 



NECTRIA DITISSIMA 1 * 



It is the dicotyledonous trees that are chiefly attacked by this 

 fungus, many of the varied forms of disease which are usually 



1 R. Hartig, Untersuchungen, I. p. 209, Plate VI. 



* [This fungus is very common in this country, and I have frequently 

 observed and examined its undoubted connection with the canker of apple 

 and other trees. ED.] 



