38 DISEASES OF TROPICAL PLANTS 



CH. 



the host plant through the stomata, branches and ramifies 

 among the cells, from which it obtains its nourishment 

 by means of haustoria. Eventually the mycelium comes 

 to the surface and forms white blisters just below the 

 epidermis. Each hypha becomes constricted, thus form- 

 ing a chain of conidia or non-sexual spores. These spores 



FIG. 23. Radish affected by white rust, Albugo Candida. (Photo by H. S. Jackson.) 



are released by the breaking of the epidermis, and are 

 then scattered by the wind. Within these spores are 

 produced the zoospores which germinate and penetrate 

 new plants. The sexual spores are produced by oogonia 

 and antheridia and remain embedded in the tissues of the 

 host plant until released by the decay of the host tissues. 

 They give rise to numerous swarm zoospores. 



