ZYGOMYCETES 105 



sporangial wall, and the monosporous members of the partial sporangia of 

 Syncephalis, do not fall under the scholastically narrow concept of conidia 

 and have been described by new terms. As none of these is very fortu- 

 nate, and as the differences really possess no important principle, it seems 

 preferable to employ here also the term conidia, which already includes 

 structures very different phylogenetically ; it is essential to keep in mind 

 that these parts have resulted by the fragmentation of extrasporangial 

 partial sporangia. 



All these phenomena, especially in genera like Choanephora and 

 Blakeslea, besides their actual interest, have a fundamental significance 

 for the comprehension of the higher fungi; for they show that the change 

 of nutritive conditions produce different types of fructifications which 

 externally are so different from each other that the determination of 

 their relationships can only be obtained in pure culture. 



The Thamnidium-Chaetocladium and the Mortierella-Haplosporan- 

 gium series penetrate the nature of the Mucoraceous fructification more 

 deeply than the Choanephora-Piptocephalis series. In the latter, the 

 number of sporangiospores remains unaltered; only they no longer are 

 endogenous in the sporangia, but are somewhat retarded and in a certain 

 sense exogenous in the germination of the partial sporangia, so that in 

 the highest forms they remain enclosed in these partial sporangia. In 

 the Thamnidium-Chaetocladium series, however, the sporangiospores 

 are numerically much reduced; their functions are assumed by the 

 sporangia and these themselves successively degenerate to conidia. 



In Thamnidium elegans the main axis possesses an apical multispored 

 sporangium which, like that of Mucor, has a columella (Fig. 64, 1 and 

 2, a). Under definite conditions dichotomous branches terminating in 

 sporangia are formed from the main axis. These sporangia, however, 

 are smaller than the terminal, have no columella, become loosened as a 

 whole from the sporangiophores and contain only a few, generally four 

 spores (Fig. 64, 2 and 4). These are liberated not by deliquescence but 

 by disintegration of the sporangial membrane. These reduced sporangia 

 are called sporangioles. The spores in both types of sporangia behave 

 similarly in their germination and further development. Under favor- 

 able conditions of nourishment, however, they are continued through 

 several generations when the sporangioles become as large and multi- 

 spored as the sporangia. Conversely, with poor nourishment the 

 terminal sporangia change into sporangioles whose spore number is 

 often reduced to one (Tavel, 1892). Since within the same species both 

 well-developed and reduced sporangia appear, Thamnidium elegans 

 corresponds to the genera Choanephora and Blakeslea in the Choanephora- 

 Piptocephalis series; only in the latter both sporangial types arise sepa- 

 rately on special sporangiophores while in T. elegans they are formed on 

 the same sporangiferous hypha. 



