RHIZOPUS NIGRICANS. 21 



The formation of the spores usually Itoofins aft(M- the columella cleft 

 is complete, althoujrh in some instances (as in PI, II, fig. S) somewhat 

 previous to that, hut always hefore the layintr down of the columella 

 wall. Spore foi-mation does not take place in the manner described 

 by Van Tieghem and Leg-er— by the sinuiltaneous differentiation of 

 plates of hyaline nong-raiudar protoplasm cutting- the spore-plasm 

 into polyhedric l)locks — nor by the progressive differentiation of such 

 plates from lines on the surface of the protoplasm, as described by 

 Bachmann (1900). In the scores of sporangia sectioned in all stages 

 ot development the writer has not found at any time even the slightest 

 indication of sucii a differentiation of the protoplasm into granular 

 polyhedric masses with nongranular plasm between. The first indica- 

 tion of the division of the spore-plasm is the formation of furrows at 

 the surface, M'hich cut progressively inward. (PI. II, tigs. 8 and 9.) 

 These furrows are not broad, as in Plloholm, nor are their sides closely 

 pressed together, as in Synchitrium. They cut in at very different 

 angles to the surface of the sporangium, and pass between, and often 

 very close to, nuclei and vacuoles. (PI. II. tig. 9.) They usually 

 branch or curve at a short distance inward from the surface, and by 

 cutting into and fusing with neighboring furrows cut out small pieces 

 of the surface layer of the protoplasm of the sporangium. These 

 pieces are almost always the detinitive spores, lacking only the walls. 

 Only a few of the larger ones are further divided up. There is no 

 uninucleated stage in the spore formation of Rhizojms, as in Pilohohis, 

 it being like Sporodinia and Phy corny ces in this respect. These sj^ores 

 are at tirst somewhat angular in shape and contain exactly the same 

 number of nuclei (2 to 6) as when ripe, there being no nuclear division 

 at any stage of their existence previous to germination. 



The nuclei of the spore-plasm during all stages of cleavage are in a 

 resting condition. (PI. II, fig. 9.) Each consists of a nucleolus, or 

 occasionalh' two nucleoli, which in my preparations is stained a deep 

 red, surrounded by a zone of evenlv granular, blue-staining chromatin, 

 the whole being liounded by a definite nuclear membrane. Both in 

 the spore-plasm and in the columella the nuclei are spherical or very 

 slightly ovoid until they begin to disintegrate. They are relatively 

 more numerous in some sporangia than in others, which may possibl}^ 

 be due to differences in the moisture supply, w^et cultures making 

 looser and more bulky cytoplasm than drier ones. 



The vacuoles of the spore-plasm, which are for the most part 

 exceedingly minute, as can be seen by a comparison with the nuclei 

 in PI, II, fig. 9, do not become angular and assist in dividing the pro- 

 toplasm here as in Piloholus and Phycomyces. They retain their 

 rounded form throughout the entire process of cleavage, even when 

 furrows cut very close to them. As previously stated, the^^ contain 

 nothing but ordinary cell sap. 



