Schwarze: Cleavage in Sporangia 151 



then dehydrated, beginning with 15% alcohol, and imbedded in 

 paraffin. The sections were cut 5 /n thick, stained by Flemming's 

 triple method, cleared quickly in clove oil, and mounted as usual. 



Olpidiopsis 



Pringsheim (45) gave us the first account of spore formation in 

 the sporangia of Olpidiopsis, a parasite, which he mistook for the 

 antheridia of Saprolegnia. He speaks of the spores as " Samen- 

 korper " and says that they are formed directly (unmittelbar), and 

 that similar phenomena may be observed in the structures which 

 we now recognize as the sporangia of Rozella and Woronina. 



In 1872, Cornu (12) published a paper in which he supported 

 A. Braun (6) in reference to the parasitic nature of Olpidiopsis. 

 He noted the appearance of large centrally disposed vacuoles, their 

 disappearance, and the formation of a foamy protoplasm. Both 

 Cornu (12) and Fisher (19) agree that the spores are formed 

 directly. 



Maurizio (36) states that cell-plates are formed in spore for- 

 mation in Olpidiopsis major. As already mentioned, Loewenthal 

 is not clear as to whether spore formation in Olpidium dicksonii 

 and Zygorhizidium willei is simultaneous or by progressive 

 cleavage. 



In Butler's (9) account of spore formation in Pseudolpidium 

 aphanomycis he states that the spore " Anlage " originate as a 

 result of "heapings of protoplasm," which are few in number as 

 compared with the number of zoospores produced. Butler com- 

 pares this stage with that Harper describes in Synchytrium, where 

 the early stages of cleavage give rise to multinucleated masses of 

 protoplasm. Cleavage fissures then extend from the vacuole to 

 the sporangial wall, the vacuolar and protoplasmic membranes then 

 rupture, and the " Anlage " swell and fuse. The sporangium is 

 now filled with a homogeneous mass. Butler states : " Five or ten 

 minutes later final fashioning of the zoospores is complete and 

 movement commences in the sporangium." Butler records cleav- 

 age furrows extending from the vacuole to the sporangium wall, 

 but he does not figure them. His figure 6C, plate 9, which he 

 interprets as a " condensation of protoplasm into heaped masses," 



