INJURIES INDUCED BY PLANTS 



97 



living cambium and cortex. It is, in fact, only able to invade 

 them when they have been killed either by frost or by the want 

 of water consequent on the 

 wood drying up centrifugally 

 under the influence of the 

 mycelium of the parasite. 



The simplest way to limit 

 the increase of the parasite 

 is to cut off and burn twigs 

 and branches that are bear- 

 ing gonidia and perithecia. 

 The immediate application of 

 tar or grafting-wax to wounds 

 of all kinds is the best safe- 

 guard against infection. 



POLYSTIGMA 



The various species of 

 Polystigma induce the forma- 

 tion of red fleshy blotches 

 on the leaves of trees belong- 

 ing to the genus Prunus. 

 Polystigma rubrunfi occurs 

 on the leaves of the plum 

 and sloe. On the under side 

 of the leaves, which in sum- 

 mer display the large deep- 

 red fleshy blotches, numerous 

 small punctures will be found. 

 These are the orifices of the 

 spermagonia, which are buried 

 in the leaf- parenchyma, and 



FIG. 45. Wood of maple containing the 

 mycelium of N. cinnabarina ; magni- 

 fied by 1 200. The vigorous mycelium, 

 a a, traverses the elements and dis- 

 solves the starch-grains, b c, first 

 attacking the granulose. As the cel- 

 lulose and the mycelial filaments, J, 

 are decomposed, a green solution ap- 

 pears in the interior of the elements. 

 The walls are much perforated, as at e e. 

 (After H. Mayr.) 



from which hooked colourless 



spermatia afterwards appear. The perithecia only occur upon 

 the leaves between their fall and the following spring. By 

 sowing the ascospores on young plum-leaves new spermogonia 

 are obtained in six weeks. The best preventive measure is to 



1 Tulasne, Selecta Ftmgorum Carpologia, II. p. 76. 



H 



