150 MICROSCOPIC FUNGI. 



found in tlie cellular tissue^ confined^ with very rare 

 exceptions, to the space between the cuticle and 

 the saCj if I may so call it^ of spiral vessels and 

 their accompanying tissue^ which_, springing from 

 the subterranean branches^ pass into the tuber, 

 making their way to the several buds disposed on 

 the surface. These spots consist at first of a quan- 

 tity of discoloured cells^ mixed more or less with 

 others in a healthy condition. The grains of fecula 

 are for a long time perfectly healthy ; the cells 

 themselves^ so far from being looser^ are more 

 closely bound together than in the more healthy 

 portions. The rusty spots soon exhibit a darker 

 tint, spreading in every direction and becoming 

 confluent ; they at length extend beyond the bar- 

 rier of vascular tissue, and attack the central mass. 

 The tuber, meanwhile, assumes a disagreeable smell, 

 decomposes more or less rapidly, other Fungi esta- 

 bhsh themselves on the surface, or in the decaying 

 mass, which emits a highly fetid odour, resembling 

 that of decaying agarics ; the union of the cells is 

 dissolved, animalcules or mites make their appear- 

 ance, till at last the whole becomes a loathsome 

 mass of putrescence.''^ 



The form of the mould itself is represented 

 (fig. 264) as exhibited under the microscope, with 

 the nodose swellings of the branches, and spores 

 attached to the tips. These acrospores are filled 

 with a granular mass, from which, as hereafter 

 described, zoospores are produced. The branching 



