76 



THE FUNGI WHICH CAUSE PLANT DISEASE 



Pythium Pringsheim '^ (p. 75) 



The mycelium is found in abundance in and about the infected 

 tissue as fine, branched continuous threads. These, in the terrestial 



Fig. 45. — Cucumber seedlings. Pots 5, 6, and 8 inoculated with Pythium. Pot 7, 

 Control. After Atkinson. 



species, bear conidia on branches which are of the same character 

 as the myceHum itself. The conidia germinate either by a rupture 



of the wall or by the formation of a 

 beak-like process through which the 

 protoplasm is extruded, after which it 

 becomes differentiated into zoospores. 

 Gemmae, very like the conidia in ap- 

 pearance, are also produced. 



The oogonia are quite like the conidia 

 and gemmae in structure but develop 

 oospores within. The oogonium is at 

 Fig. 46.— Fertilization in Py- ^^^t multinucleate but as the oosphere 

 thium showing oogonium, matures all of the nuclei except one 



anthendium, oospore, pen- . ^ 



plasm and the c? and 5 migrate toward the periphery, the neri- 



nuclei. After Miyaki. , , . • , , , 



plasm, or degenerate in the ooplasm, re- 

 sulting at maturity in an uninucleate egg. This is fertilized by 

 one nucleus from the antheridium. No sperm is differentiated. 



