26 FORMATION OF SPORES OF RHIZOPUS AND PHYCOMYCES. 



cleav^age. (PI. V, figs. 21 and 22.) So far as the writer has been able 

 to observe after a most diligent search in a ver}- large number of spo- 

 rangia in all stages of spore formation, there are never surface furrows 

 cutting into the spore-plasm at any point. The angles from the vacu- 

 oles may often be seen cutting out to the surface of the spore-plasm. 

 (PL V, figs. 21 and 23.) Furrows also cut into the spore-plasm from 

 the columella cleft and fuse with the vacuolar furrows in tlie spore- 

 plasm, and thus aid in dividing the protoplasm into spores. (PI. V, 

 fig. 22.) 



During the whole process of spore formation the nuclei are in a 

 resting condition. They are spherical, or nearly so, and are made up 

 of one or two nucleoli and finely granular chromatin within the 

 nuclear membrane. (PI. V, figs. 20-24.) They are a little larger 

 than those of RMzojms. The furrows often cut very close to them, 

 but they give no visible sign of being in any way afi'ected by the cleav- 

 age of the cytoplasm in which they lie. (PL V, figs. 21-23.) I have 

 never observed a single case of nuclear division in the sporangium of 

 Phycomyces. 



The very small vacuoles described above that have no stainable con- 

 tents do not take any part in the cleavage. They remain round through- 

 out the process, even when the furrows from the larger vacuoles cut 

 very close to them. (PL V, fig. 22.) 



As the vacuoles that take part in the cleavage become angular the 

 content becomes angular also, taking approximately the shape of the 

 vacuoles, so that its surface is parallel to the vacuolar membrane, but 

 seldom in contact with it, there being still the clear nonstainable zone 

 between. (PL V, figs. 21 and 22.) As the angles of adjacent vacuoles 

 fuse, the contents are brought in contact and fuse also, thus forming 

 a mass filling up the spaces between the spores. (PL V, fig. 21.) It 

 will clearly be seen that this mass is not protoplasm, as it originates 

 as a secretion from the vacuolar membrane deposited inside the vacuole. 

 It is homogeneous at the time the spores are formed, staining bluish- 

 brown in Flemming's triple stain and containing no nuclei or other 

 inclusions. All the cytoplasm and nuclei of the spore-plasm are 

 included within the spores themselves. (PL V, fig. 21.) 



There appears to be a considerable shrinkage of the protoplasm 

 while the cutting out of the columella and the spore formation are going 

 on, and this is followed by an increased turgidity of the protoplasmic 

 masses, but this is not so marked as in Bhlzopus and. Filoholus and 

 the spores do not become sharply angular. This increase in turgidity 

 of the protoplasmic masses is followed by a very marked enlargement 

 of the small vacuoles, which did not take part in spore formation. 

 They still, however, contain only ordinary cell sap and no stainable 

 contents. The columella wall begins to form while spore cleavage is 

 going on, and continues to thicken until the spores are nearly ripe. 



