168 



Mycologia 



taneous cleavage as it still persists in the literature of spore for- 

 mation. 



While the method of the columella formation has been studied 

 in relatively few Zygomycetes, the researches by Harper (24), 

 Swingle (50), and myself have shown that the columella is not 

 from the first a plane wall, which is subsequently pushed up into 

 the sporangium, as is so often figured and described in textbooks 

 on botany, but that it originates as a dome-shaped mass of vacuoles 

 at the inner boundary of the spore plasm. Brefeld (7) observed 

 that the columella was from the first dome-shaped. The vacuoles 

 flatten in their radial axes, fuse edge to edge, and thus delimit the 

 spore plasm from the columella plasm. In Rhisopus nigricans, 

 Pilobolns crystallinus, and Sporodinia grandis a circular furrow 

 cuts upward from the base of the sporangium to meet the cleft 

 formed by the flattened vacuoles. 



This work was conducted under the direction of Professor R. A. 

 Harper, to whom I am indebted for valuable advice, many helpful 

 suggestions, and criticisms. I am also indebted to Prof. Blakeslee 

 for cultures. 



Department of Botany, 

 Columbia University, 

 New York City. 



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Pilze. Jahrb. Wiss. Bot. 34 : 279-328. 1900. 



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1881 and 1892. 



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