Metapliyta Selaginella. 141 



We have yet to describe briefly the mode of development 

 of the sporangia and their contents, and to follow the 

 development of the embryo into the young Selaginella. A 

 word on the relation of Selaginella to the pine group of 

 plants will complete the section. 



It is needless to describe in detail the development of 

 the sporangium, since it is, broadly speaking, similar to that 

 of the fern. A tapetal layer is formed, which subsequently 

 becomes absorbed. The archesporium also forms mother 

 spore-cells, capable of developing microspores or macro- 

 spores. It would be preferable to distinguish these spores 

 by terms indicative rather of their sex than of their size. The 

 microspore is a spore capable of forming a male thallus, 

 hence it might be termed a spermospore, whilst the macro- 

 spore might be termed an ovospore, an unavoidable hybrid, 

 since the word oospore has already been given to the fer- 

 tilised ovum or embryo. 1 



The development of the spores up to this stage is alike 

 for both sexes, but here their development diverges. The 

 mother cells of the spermospores are numerous, and each 

 subdivides into four daughter cells which become the 

 spermospores in question ; the mother cells of the ovo- 

 spores are also numerous, but only one of these subdivides 

 into four daughter cells which become the four ovospores of 

 the mature sporangium, the other mother cells remaining 

 undeveloped. 



After fertilisation of the ovum by a sperm the ovum 

 rapidly segments, forming a pro-embryo, which differentiates 



the embryo-sac of the angiosperm (p. 167), and the subsequent union 

 of a portion of one daughter nucleus with a portion of the other, might 

 on this view be looked upon as a species of cross- fertilisation (resulting 

 in the more vigorous formation of endosperm) of a female nucleus by a 

 male nucleus, rather than a union of two female nuclei as suggested 

 by Marshall Ward. 



1 The term macrospore is even etymologically incorrect, since 

 naKpbs means ' long,' not 'large.' Megaspore would be more correct 

 if we must use these tei 



