118 CLASSIFICATION OF THE MICRO-ORGANISMS. 



mence the development again ; if only the aecidia exist, the 

 development begins likewise directly they are ripe, and the 

 process of germination is similar to that of the teleutospores. 

 The species of the uredineee are described according to the 

 teleutospores because these show distinct differences, while 

 the uredo and aecidium fructification essentially coincide in 

 all the species. The rust fungi occur extensively on the most 

 various kinds of phanerogams, on grasses, shrubs, and trees. 

 Moisture of the ground and of the air favours their develop- 

 ment. In the case of many rust fungi the actual alternation 

 of generation is not yet certain, and hence the independence 

 of many forms as yet reckoned as particular species is doubt- 

 ful. Where it is known it is often possible to prevent the 

 infection by preventing the development of one of the stages 

 of fructification. Thus corn-fields may be protected against 

 infection with rust by extirpating the barberry bushes in the 

 neighbourhood on which the a3cidium generation occurs. 



B. The following mould fungi, which are interesting 

 either from their frequent occurrence, or from attacking 

 at times higher animals, and even man, in the form of 

 pathogenic parasites, are worthy of note : 



PerisporiacesB. 1. Some forms of the Perisporiaceae (order : Ascomy- 

 cetes). In the fungi belonging to this family the spore 

 tubes are formed in the interior of a capsule-like fruit 

 body, the perithecium ; the latter lias no preformed 

 opening, but tears open when ripe. The perithecia are 

 very small round bodies, seldom more than 1 mm. in 

 size, and commonly immediately surround the mycelium 

 in large numbers ; their walls are for tlio most part 

 coloured, and often covered with hairs or hair-like pro- 

 cesses. In many cases the origin of the perithecium by 

 sexual fecundation may be demonstrated. In eurotium, 

 for example, short twigs develop from single mycelium 

 cells and become twisted like a screw (fig. 9, c) ; this 

 screw represents the female organ, the ascogonium. 

 From the lower part of this thread branches then grow 

 outwards along the side of the screw as far as its end, 

 and one of the branches and the upper turn of the screw 

 apply themselves to each other and exchange their con- 

 tents ; after this fecundation the male branches, the 

 jollinodia, divide and branph frequently, and thus form 

 a covering which becomes the wall of the perithecium. 



