SEXUAL REPRODUCTION 79 



These gametes grow up in contact, but are at first 

 separated at the base by the cross-wall dividing the 

 mother-cells of the gametes. A single nucleus from the 

 mother-cell passes into each gamete and undergoes karyo- 

 kinetic division. One of the resulting daughter-cells 

 passes to the apex of each gamete, where it is cut off 

 from the remaining portion of the gamete by a cross- 

 wall. At this stage a perforation appears in the wall 

 separating the two gametes, the female gamete increases 

 much in size, and the male nucleus passes .through the 

 perforation in the cross-wall and comes in contact with 

 the female nucleus. The cytoplasms of both gametes 

 combine to form the zygospore, which first forms quite 

 a thin wall; inside this the thick, several layered endo- 

 spore is slowly formed. The male and female nuclei 

 have fused by the time the zygospore has reached 

 maturity. 



The formation of zygospores in the Mucorineae has 

 been studied by Leger, and the following is his view on 

 the subject. Two gametes, often identical in size and 

 structure, and replete with cytoplasm and numerous nuclei, 

 approach each other ; the contents of each gamete is cut off 

 from its supporting hypha by a cross-wall, and the double 

 wall where the two gametes touch each other is absorbed. 

 Soon after this stage is reached the cytoplasm diminishes 

 in volume, and eventually all the nuclei disappear. At this 

 moment two groups of small spheres appear ; these bodies, 

 which are dense and granular, are termed embryogenic 

 spheres. At a later stage the small spheres of each group 

 fuse together to form a large sphere. These two spheres, 

 which become clothed with a double membrane, are called 

 embryonic spheres. At the moment of germination of the 



