MUCORALES 241 



of supernumerary nuclei. Dangeard (1906 a, b), Moreau 

 (1911 a, b, c; 1912 a, b; 1913 a, b), and Keenc (1914; 1919) 

 describe nuclear fusions in the young zygospore between many 

 pairs of nuclei, while Lendner (1908 a) and McCormick (1912) 

 find evidence indicating that only a single nuclear fusion occurs. 

 Dangeard and McCormick describe cytoplasmic bodies com- 

 parable to the coenocentrum of the Peronosporales, and the 

 latter author states that the two nuclei present in the mature 

 zygospore lie embedded in the coenocentrum. Keene, on the 

 other hand, regards these bodies as undoubtedly related to the 

 elaioplasts found in many other plants, which have for their 

 function the elaboration of oil for reserve food. They occur 

 in considerable numbers in the young zygospore, progressive 

 fusions resulting ultimately in the formation of one or two 

 large bodies saturated with oil. The mature zygospore is often 

 practically filled with oil, the cytoplasm and nuclei being confined 

 to a thin parietal layer next to the wall. Following nuclear 

 fusion it is assumed that reduction division occurs in the zygo- 

 spore before germination, but the facts have not been determined. 

 Perhaps, as described for Albugo, some species characterized by 

 a single nuclear fusion and others by a multiple fusion occur in 

 this group. It is particularly unfortunate that the extremely 

 interesting and suggestive experimental data of Blakeslee can- 

 not now be explained from cytological data. 



The order, Mucorales, as here constituted contains seven 

 families, approximately thirty genera, and about four hundred 

 described species. The most satisfactory general taxonomic 

 treatments of the group are those of Fischer (1893) and Lendner 

 (1908 b). 



Key to Families of Mucorales 



I. Sporangium when present globose to pyriform, many-spored, in some 

 genera accompanied by, in others replaced by, few-spored sporangiola 

 or unicellular conidia; zygospore formed in the fusion cell which results 

 from the copulation of the gametangia. 



A. Sporangium when present containing a columella; zygospore not 

 enveloped by a layer of interwoven hyphae. 

 1. Sporangium always formed; sporangiola and conidia lacking. 



a. Sporangial wall thin, not cutiiiizod. 



1. Mucoraceae, p. 242 



b. Sporangial wall heavily cutinized in the upper portion. 



2. Pilobolaceae, p. 251 



