PHYGOPHYTA. 



153 



fected. After fertilization eacli gorm-cell becomes covered 

 with a wall of cellulose and is thus transformed into a rest- 

 ing spore. 



271. What is given above may be taken to illustrate the 

 general mode of reproduction in the family. It presents 

 much variation in the different genera and species, and in 

 some cases the sexual organs are functionless, the resting- 

 spores forming without an actual fertilization. The mature 

 resting-spores are double-walled, the outer (exospore) being 

 thick, and the inner (endospore) thin. After a considerable 

 period of repose the resting-spores germinate by sending 

 out a tube, as in Green Felt. 



272. The Downy Mildews and White Rusts {Perono- 

 sporacem) live parasitically in the in- 

 terior of higher plants. They are 

 composed of long branching tubes, 

 whose cavities are continuous 

 throughout. They grow between 

 the cells of their hosts, and draw 

 nourishment from them by means of 

 little branches {haustoria), which 

 thrust themselves through the walls 

 (Pig. 80). 



273. The asexual spores (conidia) 

 are produced upon branches (conidi- 

 ophores) which protrude through the 

 epidermis of the host. In the 



_ _,,.- ^ . . „ ^ Fig. 80.— Showing one of 



iJowny Mildews (species OI PeronO- thehyph^ (m, m)of a Mil- 



^ dew, sending suckers (haus- 



spora, Phytophthora, Plasmopara, ^^3'''*)^^^° *Ma° nmet ^^300 

 etc.) these branches find their way tidies. 

 through the breathing-pores, and bear their spores singly 

 upon lateral branchlets (Fig. 81); in the White Rusts 



