1016 



AQUATIC PHYCOMYCETES 



them. Within the apical curvature of these hyphal tips a narrow zone 

 of hyaline very refractive material develops, which seen in optical section 

 looks like a slender crescent (Fig. 83 A, below). This substance is 

 apparently derived from the apical wall. At the same time, and often 

 before the refractive dome becomes visible, there may be detected, in 

 surface view, a vacuole immediately below the hyphal tip ; this vacuole 

 increases in size and perceptibility with the enlargement of the apical 

 material. When viewed in optical section the glistening dome appears to 

 have, shortly before the discharge of the contents, a double contour 

 (Fig. 83 B-C). With the expansion of the apical refractive material 

 protoplasmic ejection is initiated. The dilation of the refractive dome 

 keeps pace with the effluent protoplasm, and forms around it an extreme- 

 ly tenuous vesicle. This structure is never exactly spherical because the 

 somewhat flaring tip of the evacuation tube protrudes slightly into its 

 lower portion (Fig. 83 D). The ejected protoplasm appears as a smoothly 

 granular homogeneous mass which completely fills the vesicle. Imme- 

 diately after discharge a slight surging movement of the minute particles 



m 







^VP" 







m 



, mm 



/,-; ■ 



: \ 





:■ ■■ 



i 



Fig. 83. Formation of zoospores in Pythium 

 (See explanation in text, p. 1015. [Sparrow, 1931b]) 



