i9i 2] SHARP— ORCHID EMBRYO SAC 



379 



m 



Coelogyne massangeana and Pogonia macrophylla 



forms 



from a single megaspore 



As 



pollination has occurred. In most of the species here reported the 

 pollen tubes are found growing among the ovules before the pro- 

 phases of the reduction division in the megaspore mother cell; in 

 one or two species they are not present before the embryo sacs reach 

 the 2 or 4-nucleate stage. In reciprocal crosses between Phajus 

 grandifolius and Bletia Shepherdii it was found that in both cases 



great numbers 



which 



numbers but in the same manner 



tion. In no case, however, was fertilization or an embryo seen 

 resulting from crosses between these two species. Thus the 

 stimulus necessary to the development of ovules with embryo sacs 



be furnished by foreign pollen incapable of effecting fertiliza- 



tion. 



Discussion 



main 



is the variability in development within the species. It has been 

 noted by several workers that while the embryo sac of one species 

 of a genus or family is formed from the megaspore mother cell 



group 



megaspores 



within 



•served, as in Salix glaucophylla 

 (Chamberlain 4) and Juglans cordiformis (Karsten 5). In the 

 Orchidaceae the latter condition appears to hold in a number of 

 cases, the fate of the megaspore mother 



the spi 

 Epidendru 



Sharp 



Shepherdii, and recently for Epipactis p 



This fluctuation results in a reduction in the number of divisions 



occurring between 



m 



When 



