360 BOTANY. 



the conidia (Pig. 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 

 shghtly different. The conidial hyphffi 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 monilif orm 

 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.— Germination of the conidia of Perono- -i. . , ° 



mora infestans. a, conldiam after lying for some jTerOWOS/lOr'a the COn- 



tmie in water, tlie contents divided ; 0, tne rupture j.„^j.„ _.» ir, . • A' -^ 



of tlie conidium and the escape of the parts as TeniS 01 tne COniQlUm, 



swarm-spores (zoospores); c, swarm-spores, with ^l,p„ v^lapp^ nndpr tbp 



cilia ; a, swarm-spores after coming to rest, in va- " iicii jjiaucu uuuci i/iic 



rionsstagesof germination. X 390.— AfterDeBary. ppoper Conditions of 



moisture and temperature, become transformed into many 

 bi-ciliate swarm-spores (a, i, 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 hyphffi ; 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, O, 

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



