GERMINATION AND GROWTH. 



151 



FIG. 90. Pseudospore of Ustilago recep- 

 taculorurn in germination, and secondary 

 spores in conjugation. (Tul.) 



which are developed on the 



Ustilago as have been remarked in the sporules of the first 

 generation in Tilletia. 



Returning to Cystopus, as the last of the Uredines, we must 

 briefly recapitulate the observations made by Professor de Bary,* 

 who, by the bye, claims for them an affinity with Peronospora 

 (Mucedines but too well known 

 in connection with the potato 

 disease), and not with the Ure- 

 dines and their allies. In this 

 genus there are two kinds oT 

 reproductive organs, those pro- 

 duced on the surface of the plant 

 bursting through the cuticle in 

 white pustules, and which De 

 Bary terms conidia, which are 

 generated in chains, and certain 

 globose bodies termed oogonia, 

 mycelium in the internal tissues of the foster plant. When the 

 conidia are sown on water they rapidly absorb the moisture, and 

 swell; the centre of one of the 

 extremities soon becomes a large 

 obtuse papilla resembling the 

 neck of a bottle. This is filled 

 with a granular protoplasm, in 

 which vacuoles are formed. 

 Soon, however, these vacuoles 

 disappear, and very fine lilies of 

 demarcation separate the pro- 

 toplasm into from five to eight FIG. 91. Conidia and zoospores of Cys- 



, , -. . . . , to pus candidus ; a. conidium with the 



polyhedriC portions, each pre- plasma divided ; b. zoospores escaping ; 



Tixi f j.1 i J c - zoospores escaped from the conidium; 



Sentmg a little famtly-COloured d. active zoospores ;e. zoospores, having lost 



vacuole in the centre (a). Soon their cUia > <*>* to germinate, 

 after this division the papilla at the extremity swells, opens itself, 

 and at the same time the five to eight bodies which had formed 

 in the interior are expelled one by one (b). These are zoospores, 



* De Bary, " Recherches," &c. in " Annales des Sciences Naturelles " (4 me 

 Be>.), xx. p. 5 ; Cooke in " Pop. Sci. Rev." iii. (1864), p. 459. 



