296 PROCEEDINGS OF THE AMERICAN ACADEMY. 



what over fifty cell cultures were made, but the production of zygospores 

 was so little affected by the external conditions tested in the series which 

 were conducted, that it seems undesirable to give more tlian a summary 

 of the chiefly negative results obtained. In general, it may be said that 

 zygospores were produced together with sporangia on all the substances 

 tested, when the growth of the fungus was not obviously impeded. 



Thus on such widely different substances as egg albumen, solution of 

 peptone on sponge, solution of grape sugar on the same substance, and 

 horse dung, zygospores were produced together with sporangia. Con- 

 centration of the available nutrient, in so far as tested, has practically no 

 effect in determining the kind of fructification produced. On such dilute 

 nutrient as could be procured from tap water with pure agar, or from 

 sponge soaked with 0.5 per cent solution of grape sugar, with 0.5 per 

 cent solution of peptone, or even with tap water, zygospores have been 

 formed in small numbers along with a feeble development of sporangia. 

 It sometimes has happened in the nutrients enumerated, that a few 

 sporangia without zygospores were produced by the poorly developed 

 mycelium. When spores are sown in such nutrient fluids as dilute 

 prune decoction, an active fermentation takes place with an abundant 

 liberation of bubbles of gas. Yeast-like forms develop, and although 

 the mycelium generally remains submerged and septate, it may at times 

 reach the surface and produce a scanty growth of sporangia sometimes 

 accompanied by zygospores. Banana is the only substance upon which 

 sporangia alone constantly form, and apparently this substratum is unfa- 

 vorable to the growth of the fungus, for the sporangia are low in their 

 development. In van Tieghem cells especially, when the substratum is 

 disposed in a thin layer or tends to become dry, sporangia alone may be 

 formed. 



The relative humidity of the air seems within normal limits to be a 

 comparatively unimportant factor in this case, and open cultures of 

 favorable nutrients exposed to the air of the laboratory as well as 

 those placed in a sealed vessel with calcium chloride have invariably 

 formed zygospores below the luxuriant sporangial growth. Although 

 zygospores seem to be somewhat more abundant when the cultures are 

 exposed to a relatively moist air, desiccation, in the experiments tried, has 

 not been able to check their formation to any considerable extent. 



Temperatures up to at least 29° C. hinder the production of neither 

 sporangia nor zygospores, and the difference between dift'used light and 

 absolute darkness is also without influence in this connection. Except 

 in the separation culture from " schleimfluss," already referred to above, 



