INJURIES INDUCED BY PLANTS 185 



EXOBASIDIUM 



The genus Exobasidium induces the formation of character- 

 istic galls on the leaves, flowers, and stems of various ligneous 

 plants. The basidia originate on the mycelium, which is chiefly 

 intercellular, and force their way outwards betweeji^the cells 

 of the epidermis, on the surface of which they form a hymenial 

 layer. No special sporophore, in the narrower sense of the term, 

 is produced. 



EXOBASIDIUM VACCINII 1 



This parasite produces swellings on the leaves, flowers, and 

 stems of Vaccinium Vitis Idcea, V. Myrtillus, and V. uliginosum. 

 These are partly of a beautiful white colour and partly of a 

 bright rosy hue, and are to be distinguished from the swellings due 

 to Melampsora Goeppertiana by their being dusted over with the 



FIG. 117. A shoot of V. Vitis Idcea, FIG. 118. "Alpine-rose apple" on 



with the hyrnenium of E. Vaccinii Rhododendron hirsutum. 



on the leaves, a a, and in the stem. 



white spores, whereas, in the case of the latter, the lustrous 

 epidermis hides the sporogenous layer ; and further by their 

 occurring more frequently on the under surface of the leaves or 

 on the racemose inflorescence than on the stem (Fig. 117). A 

 microscopic examination at once reveals the fact that the long 

 somewhat bent spores are situated on four delicate sterigmata at 

 the apex of the clavate basidia. 



This fungus, which was formerly described as a separate 



1 Woronin, Verhandlungen der naturf. Gesellschaft zu Freiburg, 1867, IV. 



