PARASITIC FUNGI. 291 



of which give rise to zoospores, as first observed by Pre- 

 vost, in 1807. Like those of Peronospora, they move 

 about in water by means of two lash-like appendages, and 

 there germinate. When resting on the leaves of a plant, 

 they make their way by means of a germinating thread 

 into its subjacent tissues, and throw out little suckers. 

 The branched mycelium gives off 'sporangia and antheridia, 

 exactly as in Peronospora ; when ripe, the sporangia are 

 strongly warted. They fall, doubtless, with the leaves to 

 the ground, where they remain till a fitting season arrives 

 for their development. The provision made for the rapid 

 development of these parasites and for the preservation of 

 their species is truly marvellous, and sufficiently accounts 

 for the difficulty of extermination and their apparently 

 sudden dispersion, especially in wet weather." 



De Bary's observations on the germination of Uromyces 

 appendiculatus are interesting, inasmuch as they show that 

 the sporidia produce a mycelium, from which springs in 

 succession 1st, spermogonia; 2dly, peridia, producing 

 chains of orange-coloured fruit, or, in other words, an 

 JEcidium; and 3dly, the original fruit of Uromyces, ac- 

 companied by the more simple fruit commonly called 

 uredo, and now called wedo-stylospores. The germination 

 of the fruit produced 'by the peridia, as well as that of 

 the uredo-stylospoies, produces, according to De Bary, 

 1st, Uredo-stylospoies, and 2d, the original Uromyces- 

 spores. Thus we see the Uromyces-spoies passing through 

 the generations of promyceliuin, sporidia, and mycelium 

 the latter producing successively the two different products, 

 spermogonia and aBcidia, and ultimately the original fruit 

 of Uromyces, accompanied by the Uredo. The spermatia, 

 or contents of the spermogonia, never germinate ; but we 

 find the fruit of the secidia, and also of the Uredo, repro- 

 ducing first the Uredo itself, and subsequently the original 

 fruit of Uromyces. Other interesting points, noticed by 

 the same author, are, " that not only has each species of 

 parasite a certain special nutrient plant, but that in certain 

 Uredines with multiple fruit and alternate generations 

 each sort of reproductive organ buries its germ in a dif- 

 ierent nutrient plant ; and that the vegetation of the para- 

 site is the cause of the disease." 

 u2 



