INJURIES INDUCED BY PLANTS 



169 



of the leaf-fascicles that survive at the base of the shoot develop 

 into shoots, and these afterwards become diseased like the rest. 

 The fact that a pine that is once attacked by the fungus suffers 

 from the disease year after year during successive decades 

 justifies the assumption that the mycelium of the fungus is 

 perennial in the shoots. From the part of a pine wood that is 

 first attacked the focus of the disease the disease continues to 

 spread each year in a centrifugal manner. The point is to be 

 emphasized that very young woods those from one to three 

 years old suffer most from the disease. Pines that become 

 diseased at a later period are sometimes so badly crippled as to 

 hold out but faint hope of a healthy wood, but as a rule a dry 

 spring occurs sooner or later which retards the development of 

 the fungus, and so, a few years' mitigation of the disease being 

 granted, the plants gradually recover, although they again suffer 

 in unfavourable seasons. About the thirteenth year the disease 

 spontaneously disappears. Clearing out the aspens from the 

 young pine woods is the surest method of combating the disease 



Second Form on Larix europsea with Cseoma Laricis. 1 Melampsora 



Tremulse Laricis 



The larch-leaf-rust is distributed throughout the whole of 

 Germany, and is frequently so common that a large part of the 

 foliage is destroyed by the fungus. 

 It is often overlooked on account 

 of the damage bearing a certain re- 

 semblance to that due to Chermes 

 Laricis. In the month of May 

 numerous spermogonia first of all 

 .appear on the leaves, amongst 

 which the Cceoma- layers break 

 through the epidermis of the leaf 

 in the form of long or short yellow 

 cushions. 



After the spores have been shed 



the leaves wither and fall off. Felling the 'aspens in the neigh - 

 hourhood of larch woods protects the latter against the disease. 



1 Wichtige Krankheiten der Waldbaume, 1 874, p. 93, and Allgemeine Forst- 

 und Jagd-Zeitung, 1885, p. 326. 



FIG. 100. Larch-leaves attacked by 

 Caonia Laricis. 



