260 BOTANY. 



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

 considerable yariations 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 

 sHghtly different. The conidial hyphse multiply greatly at 

 certain points beneath the epidermis of the host, and there 

 produce conidia 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 



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.— Gerniiiiation of the conidia of Peronn- „ ii 

 spora infestans. a, conidium after lying for some Jr^erOnOSpora the Cen- 

 time in water, the contents cfivided ; 6, tne rupture j.„„j.„ -i! ii, - ■;]•,., 

 of tlie conidium and the escape of the parts as lentS 01 cne COniOmm, 

 swarm-ppores (zoospores); c, swarm-spores, with wlipn nlnpprl nnrlcr +>io 

 cilia ; (i, swarm-spores after coming to rest, m va- " "cu piai,eu. uuuu i/iic 

 riousstagesof germination. X 390.— After DeBary. pj^Qpgr conditions of 



moisture and temperature, become transformed into many 

 bi-ciliate swarm-spores (a, b, 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 hyphse ; in other cases it perforates the epidermis cell- 

 walls and thus passes into the interior of its host (ff. 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 s})ecies of the genus Cystopus, 

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

 Fig. 176), in the manner described above for Peronospora, 



