148 



Mycologia 



phagus Euglenae, and Butler (9) in Pseudolpidium aphanomycis 

 record spore formation as proceeding from the center to the pe- 

 riphery by cleavage, but do not refer to it as progressive. Like- 

 wise, Hartog (27), investigating Pseudospora Lindstedii, a mona- 

 dine parasitic on Saprolegnia, figures cleavage by vacuoles extend- 

 ing to the periphery of the protoplasmic mass, but does not refer 

 to it as progressive. Davis (16) figures progressive cleavage in 

 the sporangia of the alga, Derbesia, by means of furrows starting 

 from the periphery and proceeding inward. Loewenthal (35) has 

 studied spore formation in Olpidium dicksonii and Zygorhizidium 

 willei and Griggs (22) has studied Monochytrium, but both au- 

 thors leave the question unsettled whether the cleavage is progres- 

 sive or simultaneous. 



In 1899, Harper (24), studying cell-division in sporangia and 

 asci, pointed out that in the sporangia of Synchytrium decipiens 

 the cleavage is accomplished by furrows, which form on the surface 

 of the initial cell, and by growing deeper in a more or less radial 

 fashion divide the protoplasmic mass, successively, into smaller 

 portions. Harper also investigated the spore and columella for- 

 mation in Pilobolus crystallinus and Sporodinia grandis. He 

 finds, as Brefeld had stated, that the columella is not first a plane 

 wall, which is eventually pushed up into the sporangium, but that 

 it is from the first dome-shaped, a layer of vacuoles appears near 

 the inner boundary of the dense spore plasma, which subsequently 

 flatten and fuse and thus delimit the spore plasma from the colu- 

 mella plasma. In the case of Pilobolus the columella formation is 

 aided by cleavage furrows cutting in at the base of the sporangium. 



In Pilobolus, as in Synchytrium decipiens, the cleavage is pro- 

 gressive and is initiated by the formation of surface furrows which 

 deepen and finally cut the plasma into protospores. In Synchy- 

 trium decipiens the uninucleated protospores become multinucleated 

 and enlarge to form the spores which in germination again become 

 sporangia. In Pilobolus the progressive cleavage leads to the for- 

 mation of one or few nucleated protospores. These protospores 

 become multinucleated, increase in size, and divide until finally 

 oblong, binucleate sporangiospores are produced. In Sporodinia, 

 Harper finds an abbreviated process of spore formation in that the 



