xxix.] MILDEW OF PARSNIPS. 241 



At this point the fungus emerges through one of the 

 organs of transpiration as shown in Peronospora trifoliorum, 

 D.By., Fig. 1; P. parasitica, Fig. 29; and P. infestans, 

 Mont., Fig. 127. A single conidium or spore is farther 

 enlarged to 1000 diameters at A. As maturity is reached 

 the vital material within the dull-coloured, non-lustrous, 

 spores, divides or differentiates itself into several polyhedric 

 portions, and each of these portions ultimately bursts out 

 of the conidium as at B. Soon after emergence these little 

 spores become furnished with two extremely fine and 

 attenuated vibrating hairs or cilia as at C ; and with these 

 cilia the spores are able to propel themselves and sail about 

 with some rapidity over any moist surface. These zoo- 

 spores are doubtlessly carried from plant to plant by the 

 wind causing damp diseased leaves to flap against each 

 other. After swimming about for a short time the 

 zoospores burst and produce mycelium, which in turn 

 reproduces the Peronospora after entering the host plant 

 by the organs of transpiration. It is remarkable that at 

 a time when little or nothing was known of zoospores in 

 the Peronosporece that the Rev. M. J. Berkeley wrote in 

 the English Flora, 1836, under Botrytis crustosa, Fr. (a 

 synonym of Peronospora nivea, Ung.), " the spores, very 

 large and decidedly filled with sporidia, as in Mucor." 

 See the description of Mucor subtilissimus, Berk., in this 

 work. Oospores or resting -spores are produced within 

 the tissues of the host plant ; one of these, enlarged 400 

 diameters, is shown at I). 



Often associated with Peronospora nivea, Ung., especially 

 in the leaves and stems of ^Egopodium Podagraria, L., a 

 second fungus named Prot omyces macrosporus, Ung., is found. 

 The name Protomyces is derived from protos, first, and 

 mukes, a fungus ; macrosporus^ of course, means large- 

 spored. The constant occurrence of the Peronospora with 

 the Protomyces is very remarkable, but until better evidence 

 is forthcoming we are inclined to look upon the phenom- 

 enon as a striking example of " consortism." We have 

 R 



