MICHIGAN ACADEMY OF SCIENCE. 71 



ductioii that is the coiiipleiueut of the cell union. Tims the lornia- 

 tion of gemmae on the liverwort gametophyte or of the bulbils ou 

 the sporophj'tes of certain ferns is true asexual reproduction. The 

 formation of spores in the moss capsule, ou the other hand, is 

 merely the final stage of the sexual reproduction begun by the union 

 of sperm and egg in the archegone. 



The feiii type of sexual cycle persists in the still higher plants 

 with a shoving of reduction division (RD) further and further 

 towards the point of gamete production (G). Finally in the 

 Anthophyta (the flowering plants proper, as distinguished from 

 the Gymnosperms), the haploid stage represents only two nuclear 

 generations in the male gametophyte and three (sometimes less) 

 in the female gametophyte. (Fig, 8.) Thus in a very different 

 group of plants we come back to almost the same style of sexual 

 cycle that occurs in Fucus, the prevalent animal type. 



In all of the examples that have been mentioned the cell union 

 lias been followed immediately by the nuclear union. This is not 

 always the case in plants. In the Ascomyceteae, Claussen worked 

 out the cytological details from the time of entry of the male nuclei 

 into the oogoue up to the formation of the ascospores. The main 

 points are as follows: Upon the union of the club-shaped antherid 

 with the trichogyne of the oogone the numerous male nuclei pass 

 from the former into the latter and then into the oogone proper. 

 Here the male nuclei approach but do not unite with the female 

 nuclei. They arrange themselves in pairs and divide simultaneous- 

 ly. By this ''conjugate" division numerous pairs of nuclei are 

 produced and these migrate out into the ascogenous hyphae. In 

 these eventually cross walls are laid down so that each cell con- 

 tains two nuclei, one probably descended from a male nucleus and 

 the other from a female nucleus. Finally at the extremity of each 

 ascogenous hypha the two nuclei unite, forming the single, dip- 

 loid, nucleus of the voung ascus. This divides now bv reduction 

 division so that the ascus soon contains four haploid nuclei. 

 Another vegetative division of the nuclei produces the eight nuclei, 

 the number normal to this plant. About each is formed an asco- 

 spore. These ascopores produce the new plants. In the whole 

 life history of the plant there is but one diploid nucleus, the one 

 formed in the youn^ ascus by the union of the two nuclei of respec- 

 tively male and female ancestry. The threads that bear the asci, 

 the ascogenous hyphae, contain in their cells two nuclei, but these 

 are haploid. The cells of the vegetative mycelium have only hap- 

 loid nuclei. We must note, however, that the cells of the asco- 



