ZYGOMYCETES 



99 



into an easily soluble form so that in damp air it dissolves and the crystals 

 scatter. Only the base of the sporangial wall remains fixed in the major- 

 ity of genera, forming a basal collar about the columella (Fig. 54, 3). In 

 the Mortierelleae, the wall is equally soluble but the oxalate crystals are 

 lacking. In the Piloboleae it is cuticularized, except at the base, and 

 permanent. 



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Fig. 58. — Pilobolus crystallinus. 1. Young sporangium. 2. Mature. 3. Showing 

 protoplasm in young sporangium. 4. Beginning of vacuoles which later form the cleavage 

 zone of the columella. 5. Differentiation of protospores. The wall of the columella will 

 develop on the proximal side of the cleavage zone. 6. Protospores. 7. Nuclear divisions 

 in the protospores, with wall of the columella at left beyond which is the superfluous proto- 

 plasm with nuclei. 8 to 10. Development of sporangiospores from proto spores. 11. 

 Mature sporangiospores. 12. Germinating sporangiospores. (3 X 53; 4 X 20; 5 to 7 X 

 500; 8 to 12 X 830; after Brefeld, 1881, and Harper, 1899.) 



At first most of the cytological processes within the sporangium are 

 the same. The content of the young swelling is divided into a central 

 zone mainly filled by sap and penetrated by a few protoplasmic threads, 

 and into a rich peripheral zone containing most of the nuclei (Fig. 58, 3). 

 The border between the two is differentiated into a foamy protoplasmic 

 layer permeated by narrow flattened vacuoles. These fuse laterally and 

 form between the vacuolate central portion and the protoplasmic spheri- 

 cal cap, a cleavage cavity (Fig. 58, 4) ; its bordering surfaces are covered 



