LAGENIDIALES 913 



members of the Sirolpidiaceae. 1 Both Petersen (1905) and Sparrow 

 (1934c) state that the zoospores assume motility within the sporangium, 

 emerge by their own efforts, and swim away at once. In Sirolpidium 

 (Sparrow, op. cit.) the zoospores are minute, narrowly pyriform, 

 somewhat arched or bent and bear two long oppositely directed ante- 

 riorly attached flagella (Fig. 77 I, p. 967). 2 A strongly refractive granule 

 is visible in the front part of the body. In Pontisma (Sparrow, op. cit.), 

 also, the zoospores are relatively small, narrowly pyriform, and bear a 

 refractive granule at either end. The two oppositely directed flagella 

 arise near the center of the body, or possibly at the fore end (Fig. 78 D, 

 p. 969) 



In the Lagenidiaceae the process of zoospore formation strongly 

 resembles that in Pythium. The relatively large zoospores either are 

 partly formed in the sporangium, as in Myzocytium (Zopf, 1884), and 

 complete their maturation in a delicate more or less evanescent vesicle 

 produced at the tip of the discharge tube, or, as in Lagenidium raben- 

 horstii (Zopf, op. cit.), undergo their entire development within the 

 extramatrical vesicle. In the sporangia of M. proliferum, a parasite of 

 algae, Zopf noted that, coincidently with the formation of the discharge 

 tube, the protoplasm became separated by small vacuoles into approx- 

 imately like-sized portions. With the gelatinization of the tip of the tube, 

 these segments of protoplasm emerged to form a globular homogeneous 

 motionless mass at the orifice. No divisions of the protoplasm could be 

 observed at this time. Shortly, however, a slight motion of the whole 

 mass was discernible, accompanied by a contraction away from the wall 

 of the delicate surrounding vesicle. The protoplasm was then cleaved 

 into the same number of parts as was previously observed within the 

 sporangium. As separation continued, the spore origins showed individ- 

 ual motion, and underwent amoeboid changes of shape. Delicate flagella 

 became visible around the periphery (Fig. 79 A, p. 977). For a short 

 period after separation the zoospores exhibited a lively swarming 

 within the vesicle, whose delicate membrane eventually deliquesced, 

 releasing the zoospores, which swam away. In L. rabenhorstii (Zopf, op. 



1 See, however, Vishniac (1955b). 



2 Vishniac (op. cit.) found the zoospores of Sirolpidium zoophthorum to be heter- 

 ocont, with the shorter flagellum of the tinsel type. 



