THE FUNGI 



157 



In the Mildews of the genera Peronospora, Plasraopara, etc., the 

 conidia are formed singly at the ends of branching conidiophores 

 which grow out through the stomata of the host and form a delicate 

 downy coating upon the affected parts (Fig. 121, I). 



Sex-organs. Antheridia and oogonia (Fig. 122) much like those of the Sapro- 

 legniacese are found in Albugo. They arise from the deep-seated hyphse, the 

 oogoniuin and antheridium forming from separate branches. The former is a 

 globular cell filled with colorless protoplasm, and contains many nuclei. As it 

 approaches maturity, there is found a single large egg-cell, surrounded by a 

 nearly transparent layer of cytoplasm in which are numerous nuclei. In 



R 



E 



FIG. 121. A, normal capsule of Capsella, slightly enlarged. B, capsule hypertrophied 

 by the growth of Albugo Candida ; con, masses of conidia. C, leaf of Amarantus 

 with patches of A. bliti. (Natural size.) D, hypha of A. Candida, showing a haus- 

 torium, h (X 300). E, conidiophores of A. Candida (X 225). F, Germinating 

 conidia of A. bliti (x 375). G, active, H, germinating zoospores. /, conidio- 

 phore of Plasmopara viticola ( X 150) . 



A. Candida the egg-cell contains but a single nucleus, in A. bliti there are 

 many. 



The antheridium is irregular in shape and contains several nuclei. It sends 

 a tube through the oogonium wall to the egg, into which its contents are dis- 

 charged. When the egg contains but one nucleus, a single antheridial nucleus 

 fuses with it; where the egg is multinucleate, there is a fusion of each egg- 

 nucleus with an antheridial one. 



The egg now develops a wall and becomes a resting-spore (Fig. 122, D), 

 about which is developed a dark brown sculptured wall, which is deposited upon 

 it principally by the activity of the nucleated protoplasm in which the young 

 spore is imbedded. 



The resting-spores are not set free until the tissues of the host decay. They 

 germinate either by forming zoospores, or by developing a germ-tube at once. 



