260 BOTANJ. 



the conidia (Fig. 175). In the different species there are 

 considerable variations in the size and shape of the conidia, 

 and the mode of branching of the conidial hyphse, and upon 

 these many specific characters are based. 



344. In the genus Cystopus the formation of conidia is 

 slightly different. The conidial hypha? multiply greatly at 

 certain points beneath the epidermis of the host, and there 

 produce couidia by successive constrictions (B, Fig. 176). 

 The conidia remain in loose connection, and form moniliform 

 rows, in which the uppermost conidium is the oldest ; some- 

 times six or more conidia may be seen attached to each other 

 in this way, but generally the upper ones soon fall away. 

 When the epidermis of the host ruptures, the conidia appear 

 g as a powdery mass, 



which may be blown 

 away by. the feeblest 

 movement of the air. 



345. The germina- 

 tion of conidia presents 

 two modes : in some 

 species of the genus 



Fig. 177. Germination of the conidia of Perono- ,, c 

 siiora infextans. a, conidium after lying for some Pcronospord the CO11- 

 time in water, the contents divided; b, the rupture , , . ,, -j. 



time in water, the contents divided ; 6, the rupture , , . ,, 



of the conidium and the escape of the parts as tents Ot the 



swarm-ppores> (zoospores) ; c, swarm-spores, with i Til'ippd nndpr thp 



cilia ; d, swarm-spores after coming to rest, in va- v> 



rioiiBBtagesof germination, x 390.-Af ter De Bary. p ro j )cr conditions of 



moisture and temperature, become transformed into many 

 bi-ciliate swarm-spores (a, 1), and c, Fig. 177). These are 

 active for a time, after which they come to rest, their cilia 

 disappear, and a germinating tube is sent out from each 

 (d, Fig. 177), which, if properly situated, enters a stoma. 

 and in the interior of its host gives rise to a system of vege- 

 tating hyphae ; in other cases it perforates the epidermis cell- 

 walls and thus passes into the interior of its host (H, Fig. 

 176). In other species of Peronospora the conidium does not 

 break up into swarm-spores, but gives rise directly to a ger- 

 minating filament. In all the species of the genus Cystopus, 

 the conidia first give rise to swarm-spores (C, D, E, F, G, 

 Fig. 176), in the manner dcscrilx'tl above for l'er(int>x/>r. 



