BLAKESLEE. — SEXUAL REPRODUCTION IN THE MUCORINEAE. 285 



even entirely fail to develop. Althongh the matter has not been inves- 

 tigated, it is probable that this peculiarity, as in Phycomyces, has no 

 connection with the sexual differences between the two strains. 



Whether there is a mutual attraction between the hyphae from which, 

 at their points of contact, progametcs are developed, is at present uncer- 

 tain. That such an assumption is not necessary, however, to account 

 for the facts observed, is shown by the results of an experiment similar 

 to that already described under Rhizopus (p. 268). In this instance 

 bags of nutriment were freely suspended so that their opposite faces 

 were 3 cm. apart and were inoculated respectively with (+) and (— ) 

 strains of the Absidia. Zygospores formed in abundance where the 

 hyphae from the opposite strains met in the air space between the sus- 

 pended masses of nutriment and thereby showed that, if any orienting of 

 the coujugative hyphae occurs, the directive influence must lie outside 

 the substratum and -in the hyphae immediately affected. 



Sufficient evidence is not at present available to determine the relative 

 abundance in nature of the {+), (—), and neutral strains. Of three 

 additional strains of this species derived from different sources, however, 

 one is weakly (— ) in character, and two are apparently neutral. 



MUCOR N. 



This heterothallic species, which is the type of a new genus, was 

 found by Professor Thaxter together with its zygospores on a laboratory 

 culture and kindly given the writer for experimentation. 



External factors have more influence on zygospore formation in this 

 species than in most of the other heterothallic forms under cultivation. 

 At the room temperature under rather dry conditions, a zygosporic line 

 is slow and feeble in development. If, however, the cultures are con- 

 ducted in a nearly saturated atmosphere, zygospores are more abundant, 

 while, in the warm oven at 26°-28°C., the line is decidedly thicker and 

 earlier in appearance. Concentrated nutrients, in so far as they have 

 been tried, fail to yield zygospores. 



When contrasted, the (+) and (— ) strains show a striking dift'erence 

 in habit which readily enables one to distinguish them. The growth of 

 the (— ) strain is lower and almost white, while that of the (+) strain is 

 higher and dirty yellow in color. These differences between the (+) 

 and ( — ) strains as well as their sexual character have remained un- 

 changed through sixteen sporangial generations. 



