160 



Mycologia 



inwardly and as the spore plasm is giving of! water the clefts 

 widen. The furrows from the surface appear to cut into the spore 

 plasm in a centripetal fashion. They meet and fuse with those 

 furrows which started from the columella cleft and cleavage is 

 thus completed ; the protoplasm has been cut up into a mass of 

 irregular blocks which are variable in size and are multinucleate. 

 These spore initials represent, as compared with swarm spores of 

 Saprolegnia and the protospores of Synchytrium decipiens, Pilo- 

 bolus crystallinus, Circinella conica, etc., a premature completion 

 of spore formation. They correspond to the multinucleate masses 

 preceding the protospores. As in Rhizopus nigricans, the spores 

 of Sporodinia grandis are multinucleate at their inception. When 

 cleavage is complete the spore initials present a dense granular 

 appearance. The protoplasmic mass is also somewhat shrunken. 

 Soon, however, the spore initials take up water and grow, the 

 protoplasm becomes less granular and takes on a lighter stain. 

 The spores become so tightly pressed together that their proto- 

 plasmic membranes assume polyhedral outlines, which are so thin 

 that they are traced with difficulty under the oil-immersion objec- 

 tive (PI. 15, fig. 4). This stage is homologous with the so-called 

 homogeneous stage, which Strasburger and Biisgen described for 

 Saprolegnia. This period of growth is followed by a second con- 

 traction. The spores now develop a thin wall, contract slightly, 

 and round up. 



I have illustrated the chief stages of the development of the 

 columella and spores in Sporodinia grandis in a series of text 

 figures (text fig. C, 1-5). 



Fig. C. Diagrams showing the method of the columella and spore forma- 

 tion in Sporodinia grandis, the nuclei appearing as mere dots, i, a young 

 sporangium. 2, showing the dome-shaped layer of vacuoles outlining the 

 columella. 3, showing early stage of progressive cleavage. 4, showing the 

 polyhedral stage. 5, mature spores. 



