APOMIXIS AND RELATED PHENOMENA 



403 



may occur, giving unreduced megaspores (Marsilia), or only one division 

 may take place {Taraxacum), or the gametophyte may arise from the 

 megasporocyte itself without haplosis (Antennaria) . 



B. Apogamy. — The apomictic development of a sporophyte from a 

 cell or cells of the gametophyte instead of from a gamete. 



1. Reduced Apogamy. — The developing cells have nuclei with the 

 reduced (gametic) chromosome number. 



[Called haploid apogamy by Hartmann, generative apogamy by Winkler, haploid 

 apogamety by Renner, and meiotic euapogamy by Farmer and Digby.] 



The development of sporophytes from vegetative tissue of gameto- 

 phytes with the reduced chromosome number and without nuclear fusion 



Fig. 226. — A, nuclear migration in gametophyte cells of Lasiraea. (After Farmer and 

 Dighy, 1907.) B, section through gametophyte, showing young sporophytic tissue (s) 

 developing from gametophytic tissue (g). (After Farmer and Digby.) C, sporophyte 

 arising apogamously from gametophyte in Pteris cretica; b' , first leaf; v, stem apex; w, 

 root. (After de Bary.) 



has frequently been observed among ferns. ^ The process commonly 

 begins with the division of the gametophytic cells to form a mass of 

 "engrafted tissue" which then grows into a new sporophyte (Fig. 226, B). 

 Ordinarily, apogamy is offset in the life cycle by apospory. In Nephro- 

 dium hirtipes the spores are formed, though in an abnormal manner: 

 when there are eight sporogenous cells in the sporangium there is an 

 incomplete nuclear division, each nucleus coming to have the unreduced 

 number of chromosomes. These eight cells then function as sporocytes 



^ E.g.: Lastrcea pseudo-mas, var. cristata apospora (Farmer and Digby, 1907); 

 Nephrodium molle (Yamanouchi, 1908c); and Nephrodium hirtipes (Steil, 1919o). 



