224 



A TEXTBOOK OF THEORETICAL BOTANY 



of the Fungus and also the production of zoospores. The tip of a hypha 

 swells up and develops into a zoosporangium, which is then cut off by a 

 septum (Fig. 214). When the zoosporangium is mature a papilla is formed 

 either at the apex or from the side of the sporangium. It is at first tubular, 

 but later swells out at its distal end to form a vesicle. Into this the contents 

 of the sporangium pass in a partly differentiated state, and in the papilla 



fO;,,. PAPILLA 

 '\ '' t 



VESICLE 



DEVELOPING 

 ZOOSPORES 





EMPTY 

 ZOOSPORANGIUM 



ZOOSPORANGIUM 



A B 



CONIOIOSPORES 



YOUNG HYPHA 

 \ 



FLAGELLUM 

 ZOOSPORE 



ZOOSPORE 



DEVELOPING - 

 HYPHA 



Fig. 214. — Pythiuni. Asexual reproduction. A to D, Pythium caroUnianum. 

 A, zoosporangium. B, Formation of vesicle. C, Migration of the cytoplasm 

 into the vesicle. D, Differentiation of zoospores. E, Zoospores. ¥, Pythium 

 proliferum. Germination of zoospores. G, Pythium intermedium. Formation 

 of conidiospores. 



zoospores are formed. They are reniform with two lateral flagella. The 

 vesicle then breaks and the zoospores swim away in the water film. It some- 

 times happens that the sporangium functions as a conidiospore, and instead 

 of forming zoospores grows out directly into a germ tube which produces a 

 new hypha. In this way a new mycelium develops without the intervention 

 of swimming spores. This provision enables reproduction to take place 

 under relatively dry conditions where there is insufficient moisture for 

 zoospores to swim in. 



Sexual Reproduction 



The sex organs are developed within the tissues of the host, and consist 

 of antheridia and oogonia (Fig. 215). They appear at a late stage in the life- 

 history of the Fungus, when the food material of the host is nearly exhausted. 

 The oogonium is developed from the tip of a hypha into which some of the 

 protoplasm, together with a number of nuclei, migrate and are cut off by a 



