Pteridoph ytes Lycopodiales 



225 



It is hard to stain the cell walls of the male gametophyte. Anilin 

 blue is as good a stain as any. 



The young embryo, with its two cotyledons, its root, and the 

 megaspore still attached, makes an instructive preparation when 

 mounted whole in Venetian turpentine. 



FIG. 74. Selaginella apus: longitudinal section of strobilus showing a microspo- 

 rangium with germinating microspores on the left; on the right, three of the four mega- 

 spores with gametophytes 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. 



Isoetes. -This genus is widely distributed and 13 of its 60 species 

 occur within the Gray's Manual range. 



Vegetative structure. --The short, thick stem, even in old plants, 

 cuts easily in paraffin. Fix in formalin alcohol and stain in safranin 

 and light green. Sporelings with stems about 2 mm. in diameter and 

 young plants with stems up to 5 mm. in diameter are best for a 

 study of the peculiar vascular system of this plant. 



