268 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



through the osmotic activity of the hy[)hal contents. If the surfaces of 

 two merabranes in contact become drj- there can be no mutual osmotic in- 

 fluence between the fluids contained within them, and it is for this reason, 

 perhaps, that progametes fail to form in a relatively dry air. There are 

 no doubt other causes active, however, an investigation of which the 

 writer ho[)es to undertake later. The evident advantages of small sten- 

 ders with close-fitting covers, over large ones with covers that are Igose 

 as well as soft over hard agar in connection with zygospore cultures, is 

 probably also due to their influence upon the moisture content of the air. 

 In order to test the condition necessary for transmission of influence 

 and to determine whether it acts through air or through the solid and 

 moist medium of cultures the following experiment was devised. From 

 the cover of a battery jar, the air in which was rendered moist by a lining 



of wet filter paper, two bags of cheese 

 cloth containing the substratum (bread 

 soaked in dilute orange juice) were 

 suspended by threads so that they hung 

 free with their inner faces 1 \ inches 

 apart, as is shown in the accompanying 

 diagram. The bags were inoculated 

 with opposite strains, and the appara- 

 tus was placed in the dark. In one 

 week zygospores had formed in abun- 

 dance where the aerial growth radiating 

 from the bags of bread had come in 

 contact. In this experiment any influ- 

 ence upon the origin or direction of 

 growth of the zygophoric hyphae which 

 might have been exerted through the solid culture medium, or which 

 was due to a contact of the masses of vegetative mycelia, w^as eliminated, 

 and any such influence, if it existed, must have been confined to the 

 aerial branches. If there is an ori<yiting of the zygophoric hyphae, 

 which cannot in any case be a well marked phenomenon in this species, 

 the directive influence must lie outside the substratinn and in the hyphae 

 affected. 



Differentiation between (+) and ( — ) Strains. 



In view of the fact that in a majority of the heterothallic forms inves- 

 tigated a morphological differentiation is, as has been previously men- 

 tioned, more or less well marked between (-f ) and (— ) strains, it was 



