Schwarze: Cleavage in Sporangia 165 



protracted. The spore plasm is cut up, by progressive cleavage, 

 into uninucleate protospores. An embryonic stage now intervenes, 

 the protospores grow and become multinucleate. By a series of 

 divisions binucleate definitive spores are produced. 



For the sake of comparison I have also included diagrams of 

 Rhizopus nigricans and Pilobolus crystallinus, showing stages of 

 the development of the columella and spores. 



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

 tion in Rhizopus nigricans, i, a young sporangium. 2, showing the dome- 

 shaped layer of vacuoles outlining the columella. 3, showing early stage of 

 cleavage. 4, showing the contraction stage. 5, expansion or polyhedral stage. 



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

 tion in Pilobolus crystallinus. 1, a young sporangium showing dense spore 

 plasm. 2, showing the dome-shaped series of vacuoles and a circular furrow 

 which cut out the columella. 4, stage of uninucleate protospores. 5, poly- 

 hedral stage. 6, ripe spore stage. 



Discussion 



Although a number of recent papers by Kusano (32), Barrett 

 (3), and Griggs (23) report the occurrence of simultaneous cleav- 

 age in the sporangia of certain algae and fungi, the evidence to 



