714 



FUNGI 



Oomycetes previously mentioned, in that its conidia and 

 sporangia are arranged in chains (Fig. 239), 

 instead of singly at the ends of the repro- 

 ductive hyphae. Conidia, zoospores and 

 oospores are also produced. 



The commonest species, Albugo Candida 

 Kuntz. ( = Cystopus candidus Pers.), attacks 

 cruciferous plants all over the world, and 

 is especially abundant on the leaves, stems 

 and fruit of shepherds' purse, which it 

 deforms. 



The conidia and sporangia are produced 

 Fig. 239.— Conidiophores in great numbcrs beneath the epidermis 



ox CystojiuscatididusVen^., - , , . . 



with chainsof conidia. (En- of the mfected plants, causing white 



larged 200 diameters.) , . ^. , , 



porcelam-like patches on the various parts 

 attacked, hence the name ' White Rust ' applied to this disease. 

 After a time the epidermis is ruptured and the spores escape 

 and become distributed by the wind and rain. It appears that 

 the parasite can only effect a successful entrance into shepherds' 

 purse through the cotyledons, so that old plants are not infected 

 by the spores. 



The Oospores, which have a thick warted or wrinkled coat, are 

 not formed by the fungus when parasitic on shepherds' purse, but 

 appear in abundance on other cruciferous hosts. 



Ex. 287. —The student should be made practically acquainted with the form 

 of the conidiophores, conidia, and oospores of Bremia laclucas, and the com- 

 mon species of Peronospora on Leguminosx, Cruciferae, and onions. 



Ex. 288. — Examine specimens of ' white rust ' I^Albugo) on shepherds' purse. 

 Observe the deformities produced and the smoothness of the white patches. 

 Cut sections through a white spot on the stem and examine in water with 

 a high power. Make drawings of the conidia and mycelium in the stem 

 tissues. 



