136 MORPHOLOGY 
vegetative tissue of more primitive gametophytes. The antheridium 
initial produces an antheridium with the usual jacket of sterile cells 
investing sperm mother cells (fig. 306). At maturity the jacket cells 
break down and the mother cells (with their sperms) are free in 
the general cavity of the microspore (fig. 307). The male gameto- 
phyte, therefore, is reduced to one vegetative cell and one anthe- 
ridium ; and encased by the old microspore wall it is carried to the 
megasporangium, in which the female gametophytes are developing. 
There the male gametophyte bursts through the microspore coat (fig. 
307). The sperms are very small, with more or less spirally coiled 
bodies and two terminal cilia. Selaginella thus shares with Lycopodium 
and Phylloglossum the character of producing biciliate sperms, a type 
characteristic of bryophytes, and in strong contrast with the sperms 
produced by other pteridophytes. 
Female gametophyte. The female gametophyte is much more ex- 
tensive than the male gametophyte, but the greater part of it is in- 
vested by the old megaspore wall (fig. 
308). The nucleus of the megaspore 
begins a series of divisions that continue 
until a large number of free nuclei are 
produced. This free nuclear division 
occurs chiefly in the apical (pointed) end 
of the megaspore, and results in a layer 
of nuclei, which later become invested by 
walls. Subsequent divisions result in a 
cushion of cells at the apex of the mega- 
, spore, while the large body of the mega- 
of Selaginella: the apical cushion ' * 
of cells having broken through the spore is free from cells, acting as a great 
heavy megaspore wall; an arche- food reservoir (fig. 308). The wall of 
gonium to be observed at the ape*. h me gaspore cracks at the apex and 
After Miss LYON. 
the apical tissue protrudes, developing a 
more or less expanded mass of tissue in which archegonia develop 
(figs. 308, 309). Later, the deeper region of the megaspore becomes 
filled with a tissue of large cells, and continues to act as a food reservoir 
for the developing embryo. This early differentiation of the female 
gametophyte into two distinct regions, one that produces archegonia, 
and the other nutritive, is a marked feature of the female gametophyte 
in all heterosporous plants. 
Fertilization. The male gametophytes enclosed by the old micro 
