INJURIES INDUCED BY PLANTS 



129 



mentous mycelia. Subsequently they appear to increase by 

 budding. 



It is very desirable that foresters, especially in sandy districts, 

 should direct their attention to the occurrence and biology of 

 this parasite. 



The term "Soil Canker" has been used for twenty years to 

 designate all those diseases in young and old woods where no 

 indications above ground can be referred to as a cause. Such 

 diseases have their seat below the surface, and gradually 

 spreading from the first point of 

 attack they occasion blanks and 

 gaps in woods and nurseries. 

 During the last twenty years I 

 have described a whole series 

 of parasitic fungi which induce 

 such diseases. These include 

 Agaricus melletts, Trametes ra- 

 diciperda, Polyporus vaporarius, 

 Rosellinia quercina, DematopJiora 

 necatrix, and Phytophthora om- 

 nivora (in the narrow sense). 

 To these must now be added 

 Rhizina undulata. 



The various species of Vac- 

 cinece are attacked by parasites 

 of the genus Sclerotinia. 1 The 

 gonidiophores appear in spring 

 on young leaves and stems, which 

 consequently become brown, in 



the form of a mould-like covering which emits an almond- 

 like perfume. The insects that are thereby attracted con- 

 vey the gonidia to the stigmata of the flowers of the 

 Vaccinece. A sclerotium is formed in the berries, which be- 

 come brown, dry, and " mummified " and drop off, and from 

 them there develop in the following spring one or two 

 long-stalked chestnut brown cup- like ascocarps. The ejected 

 ascospores infect the young shoots, and again produce the 

 gonidium-bearing form. 



1 Woronin, Ueber die Sdcrotienkrankheit der Vaccinienbeeren, 1888. 



K 



FIG. 70. Mycelium of Rhizina from 

 the cortex of the silver fir. a, a 

 filament of average thickness ; 

 6, very thin filaments ; c, gonidia 

 resembling Micrococcus. Magni- 

 fied 1500 times. 



