PTERIDOPHYTES—LY COPODI ALES 
249 
sporangium. Such a structure satisfies the definition of a seed. 
Ordinarily, to get the later stages, shake the spore out from the older 
strobili into a Petri dish with the bottom covered by several thicknesses 
of wet filter paper. There is enough nutritive material in the, spores 
to carry them up to the sperm and egg stage. The female gameto- 
phytes within the old spore coats generally orient themselves in the 
Fig. 79 .—Selaginella apus: longitudinal section of strobilus showing a microsporangium 
with germinating microspores on the left; on the right, three of the four megaspores with gameto- 
phytes near the archegonium initial stage; fixed in formalin alcohol, cut in paraffin, and stained 
in safranin and light green; from a preparation by Dr. W. J. G. Land. X80. 
paraffin, the base of the spore being down and the archegonium end 
of the gametophyte being up. A little of some nutrient solution, 
added to the water, will carry the development up to the cotyledon 
stage. The young embryo, with its two cotyledons, its root, and the 
megaspore still attached makes an instructive preparation when 
mounted whole in Venetian turpentine. 
