78 



COMPARATIVE MORPHOLOGY OF FUNGI 



number of conidia formed per square centimeter of infected leaf surface 

 is about three million. 



In contrast to variability of the conidiophores, the conidia appear 

 approximately the same. They are spherical, ellipsoidal or ovoid, 

 hyaline with a smooth, hyaline, brownish or dirty violet membrane. 

 In most genera a short germ papilla is present at the top. Under certain 

 conditions, the conidia of Pythium may thicken their wall and remain 



Fig. 47. — Basidiophora entospora. a, two conidiophores emerging from a stoma; st, 

 short sterigma which forms a conidium ; b, conidium with apical papilla and remains of 

 stalk; c, zoospore from germinating conidium; d, oogonium with mature oospore, whose 

 exospore is ridged. Empty antheridium at the right, (a X 230; b X 540; c, d X 550; 

 after Roze and Cornu.) 



capable of germination up to 11 months. In some species of Albugo, the 

 wall is thickened equatorially, forming a ring (annulus). Furthermore, 

 in Albugo the first conidium of a chain is generally larger than the others 

 and has a membrane of even thickness. When such a conidiophore, by 

 raising the epidermis from the tissue, breaks out of the host and the 

 spore chains break up, these first conidia remain clinging to the epi- 

 dermis of the host. Possibly these serve exclusively to raise the epi- 

 dermis and are not capable of germination. Therefore they are called 

 ''buffer cells." 



