8o TEXT-BOOK OF FUNGI 



zygospore the two embryonic spheres lose their membrane, 

 increase in size, and fuse together. At this stage nuclei 

 appear in the mass formed by the two fused embryonic 

 spheres, and undergo karyokinetic division before they pass 

 into the germ-tube. Leger says that azygospores present 

 exactly the same phases of development as zygospores ;.the 

 only point of difference being that in azygospores only one 

 embryonic sphere is present instead of two, as in the 

 zygospore. 



The above account leaves much to be desired respecting 

 the behaviour of the nuclei. Grtiber has examined 

 Sporodinia grandis and considers the presence of Leger's 

 embryonic spheres as doubtful. The subject of sexuality 

 in the Mucorineae has quite recently been prosecuted from 

 a new standpoint by Blakeslee. This author observed that 

 some species, as Sporodinia grandis, could be readily 

 induced to produce zygospores on a suitable substratum 

 by sowing spores from a single sporangium. On th other 

 hand, it was found that many other species, of which 

 Rhizopus nigricans may be taken as a type, would never 

 form zygospores from the product of a single sporangium, 

 but only when a mass of spores from a zygosporic culture 

 was used. When isolated cultures of the last-named 

 species were grown in proximity on nutrient agar, it was 

 observed that zygospores were formed at the junctions of 

 the two colonies. This suggested the idea that this species 

 consisted of two strains or races which, when grown apart, 

 produce only sporangia, but which produce zygospores 

 when the two physiologically different races are grown in 

 contact. These are designated respectively x and 

 strains, which is considered as non-committal as to 

 the sexual relation the strains bear to each other. This 



