166 



Mycologia 



prove the existence of this method of spore formation is inade- 

 quate. On the other hand, there is an accumulation of evidence 

 which confirms the contention that cell-division in the sporangia of 

 algae and fungi is essentially a process of furrowing either from 

 the periphery of the sporangia or from the vacuoles in the interior 

 of the spore plasm. 



As far as I am aware Rothert, studying spore formation in the 

 sporangia of Achlya and Saprolegnia, was the first to note the 

 contraction and expansion phases during the cleavage process. 

 His observations are, therefore, of paramount importance for 

 understanding the mechanics of the cleavage phenomena in other 

 sporangia. 



A complete parallelism with the phenomena described by Rothert 

 is found in the process of oosphere formation in Vaucheria, as 

 described very carefully from living material by Oltmanns (39). 

 Oltmanns confirms and amplifies the observations of Thuret, rela- 

 tive to zoospore formation in Vaucheria, and Strasburger and 

 Berthold, who studied the process of zoospore and oogonium for- 

 mation. 



' According to Oltmanns, just before the cell-division, which cuts 

 off the oogonium from the parent filament, there is an extrusion 

 of water from the protoplasmic mass within the oogonium; the 

 extruded water forms a large vacuole at or below the base of the 

 oogonium (figs. 8-10, pi. 6-7). This stage is comparable to the 

 first contraction phase with its large central vacuole and the for- 

 mation of radial furrows beginning the delimitation of the spores, 

 as noted by Rothert in Saprolegnia. In the case of Vaucheria, 

 cutting off of the oogonium is first initiated by what may be called 

 the cleavage vacuole. The condition is similar to that found in 

 columella formation in Pilobolus crystallinus, Rhizopus nigricans, 

 Phycomyces nitens, Sporodinia grandis, Mucor mucedo, etc. Such 

 basal vacuoles play the same role as the cleavage vacuoles which 

 appear in the spore plasm of Pilobolus, Phycomyces, Circinella, etc. 



The plasma membrane about the basal vacuole in Vaucheria is 

 finally broken, the cell-sap escapes, and the oogonial protoplasm 

 now expands ; the basal plasma membrane of the oogonium and 

 the plasma membrane of the filament are brought into close prox- 



