PEEIDERMIUM. 



415 



branch, the living portions of the ring grow on with increased 

 vigour, and even attempt to close over the injured portion. 

 This irregular growth, continued in many cases for years, pro- 

 duces abnormal cross-sections (Fig. 248). The mycelium 

 grows out centrifugally from diseased spots, so that the wounds 

 continue to enlarge, and the disease becomes easily noticeable 

 on account of the deep channels and distorted swellings on 

 the pine branches and stems. As the disease spreads inwards 

 into the stems, the conduction of water is interfered with and 

 the branches above such wounds dry up and die off. Whereas 



Fia. 2i7.—Peridci-mium pini (cai-Hcola). a, a, Mycelial stroma developed in the 

 rind ; the host-cells have become isolated from each other and contain 

 haustoria, h, of the fungus, b, Basidia composed of much smaller cells than in 

 the needle-inhabiting aecidia. jp, The peridium. (After R. Hartig.) 



young plants soon succumb to attack, the struggle with old 

 trees may go on for years. Fresh infection of older stems 

 occurs generally in the higher parts of the tree, where the 

 bark is still thin. 



Pycnidia (spermogonia) are developed between the rind- 

 parenchyma (periderm) and cork, generally towards the margin 

 of diseased spots. The conidia emerge from the ruptured 

 cork-layers of the bark as a honey-sweet liquid. H. Mayr 

 states that this liquid is given off in such quantity from 

 species of Peridermium in Japan, that it is collected and 

 eaten by the natives. 



