P.IM.-JT. . V.P.H.l.-lOl. 



FORMATION OF THE SPORES IN THE SPORANIilA OF RHIZOPUS 

 NIGRICANS AND OF PHVCOMYCES NITENS. 



HISTORICAL. 



Althouoh the lifo history unci uross uiuitomy of nearly all the species 

 of the :Mucorinea' have been carefully worked over and described, yet 

 in regard to the cytological details there are the widest differences of 

 opinion, chiefly owing to the fact that only a few forms have been 

 studied with the aid of the most recent methods. It seems desirable, 

 therefore, that others should be critically examined. The present 

 paper is a contribution toward that end. 



The earliest account that deals specifically with the formation of the 

 spores in the Mucorinete is that of Corda (1888). He investigated the 

 development of the sporangia of Rhhopm nigricans, but was able to 

 discover little of the real nature of the process. After the formation 

 of the columella in the lower part of the sporangium, he describes the 

 spores as being formed in rows radiating from the columella, but just 

 how they originate he does not make clear. 



Van Tieghem (1873, 1875, 1876) in a series of classic papers has 

 covered practically the entire group, describing the structure and 

 development of a very large number of forms with much accuracy and 

 minuteness of detail. He believed that the method of spore formation 

 was the same in all the genera having a spherical sporangium. In 

 these forms the sporogenous protoplasm separates itself into two very 

 different substances— the sporal protoplasm which is always granular, 

 and the intersporal protoplasm which is homogeneous and brilliant. 

 The sporal protoplasm has the form of small polyhedric portions, and 

 these are separated from each other by the intersporal protoplasm. 

 Soon the polyhedric masses round themselves off, secrete a cellulose 

 wall, and acquire the homogeneous refringent appearance which char- 

 acterizes the spores of the greater number of the Mucorineae. At the 

 same time the intersporal protoplasm distributes itself so that it occu- 

 pies all the space between the spores, and forms a layer between the 

 peripheral spores and the sporangium wall. Van Tieghem considers 

 this a process of free formation similar to that which occurs in the 

 ascus, differing chiefly in the amount of intersporal protoplasm. 



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