MORPHOLOGY OF THE SEED 159 



the embryo proper, while the remainder acted either as 

 a temporary storehouse of reserve or as a haustorium, 

 while several workers, such as Strasburger, Hegelmaier, 

 and Ganong, brought to light cases of polyembryony, 

 where accessory embryos sprang from the synergidae, 

 from the antipodal cells, or even from the cells of the 

 nucellus. True parthenogenesis, or the formation of an 

 embryo from an unfertilised ovum, was recognised by 

 Juel, in 1898, in Antennaria. 



To sum up, you will see that the net result of the 

 labours of a generation of workers was to show that a 

 seed was a structure in which three generations were 

 represented, one sexual and two asexual. The testa, 

 replacing the ovular integuments, was a product of the 

 primary sporophyte, while the nucellus was a solid 

 megasporangium in which only one megaspore was 

 functional. Within the megaspore arose a gametophyte 

 with a much reduced archegonium, from whose ovum, 

 after fertiUsation, there developed in part an embryo, 

 the sporophyte of the second generation. Whereas, in 

 the fern, a spore gave rise to an independent gametophyte 

 with both male and female organs, in Selaginella there 

 were two types of spore, one, the microspore, developing 

 a greatly reduced male gametophyte, and the other, the 

 megaspore, forming an almost equally reduced female 

 gametophyte, both of which, as a protection from the 

 plant's great enemy, drought, were endosporal in the 

 development. In by far the greater number of species 

 of Selaginella both microspores and megaspores when 

 ripe escape from their respective sporangia, and fertiUsa- 

 tion is effected after dispersal, but in comparatively rare 

 cases the megaspore is fertiUsed before dispersal. In the 

 Cycad the microspores still escape, but the megaspores 

 are retained permanently in the sporangium, whose wall 

 has taken on a nutritive function, necessitating the 

 development of a new ovular integument. The micro- 

 spores have thus to be transported to the micropyle. 



