22 FORMATION OF SPORES OF RHIZOPUS AND PHYCOMYCES. 



After the surface furrows have cut inward for a considerable dis- 

 tance, a few similar furrows begin to cut outward from the columella 

 cleft, which as yet contains no wall. (PI. Ill, fig. 10.) With the 

 meeting of these two systems of furrows the cleavage is practicall}'^ 

 complete. 



During the process of spore cleavage the protoplasm is slightlN' 

 shrunken, apparently because of the giving off of water. Th(^ furrow's 

 are more or less open and filled with clear cell sap only. (PL II, 

 fig. 9.) As soon, however, as the cleavage is complete, the spore 

 mass becomes strongly turgid again, and each spore so increases in 

 volume that all are pressed tightly together • and the furrows are 

 entirel}^ closed, so that with the Zeiss 2 mm. immersion objective, 1.30 

 aperture, and No. 18 compensating ocular, they appear in optical 

 section as single lines and are ver}" hard to trace through the dense 

 spongy cytoplasm. The spores are thus made sharply angular, but 

 later the}'' round oft', leaving little spaces between them. 



The formation of the columella wall usually begins before the spores 

 are entirely cut out, but it does not reach its definitive thickness until 

 the}^ are nearly ripe. 



As seen in PI. Ill, fig. 12, these spores have no regular system of 

 arrangement whatsoever, and the writer can not find the slightest 

 ground for Corda's view that they are in i-adial rows. 



As already stated, the spaces between the spores contain at first 

 absolutely nothing except cell sap. There is no trace of any inter- 

 sporal protoplasm, such as has been described by the earlier authors 

 and considered as homologous with the epiplasm of the ascus. 



The spores of B.}uz(>pu>< are at first angular and covered l)y only a 

 plasma-membrane, but soon round off and a firm wall is formed 

 about them. 



During this process of ripening a homogeneous slime is excreted by 

 the spores, w^hich fills up the spaces betw^een them. In such exposures 

 to the triple stain as best bring out the cytoplasmic and nuclear 

 structures this intersporal slime does not stain at all, and for this 

 reason the writer has left it an empty space in PI. Ill, fig. 12. By 

 a longer exposure to the violet it is readily brought out as a smooth 

 bluish mass filling up the spaces between the rounded spores. 



There is no special mechanism for the discharge of the spores in 

 Bhizo2?us 2iii in PlJohAm. There is, however, an inner layer of the 

 sporangiuDi wall that can not readily be differentiated from the rest 

 of the wall in specimens fixed in the killing fluids of Flemming and 

 Merkel; while in those fixed in Eisen's fluid and stained in the triple 

 stain it is verj^ readily distinguishable from the outer layer b}^ its 

 lighter blue color, the boundary between the two being sharply 

 defined. PI. II, fig. 7, is therefore the only one in the writer's series 

 in which he could show the separate layers of the sporangium wall. 



