FERNS AND MOSSES. 153 
streaks placed on each side of the mid-rib of the simple leaves, a narrow 
flap-like indusium arising from one side of each sorus. In the common 
polypody (Polypodium vulyare), which is abundant on old tree-stumps, 
the large sori are situated somewhat as in male fern but are devoid of 
indusia. Some ferns have two kinds of leaves, barren fronds which 
bear no sporangia, and differently shaped, fertile fronds upon the backs 
of which they are produced. 
COMPARISON OF FERN AND FLOWERING PLANT, 
In order to understand the relation which exists between the 
life-history of a fern and that of a flowering plant, it is neces- 
Fig. 65.—Selaginella [C, D, F, after Pfefer]. A. Fertile shoot (x4) in the upper part 
of which microsporangia are seen. B. Microsporangium (x 40), diagrammatic. C. 
Male prothallus (x 650) within the microspore ; v.c. vegetative cell; the remaining 
cells constitute the antheridium. D. An antherozoid (x 1400). E. Macrosporangium 
(X30), diagrammatic. F. Female prothallus (x80); w. ruptured wall of macro- 
spore. Three archegonia are represented, imbedded in the projecting part of the 
prothallus ; the central one contains a good-sized embryo, the parts of which are 
lettered 7., st., ct., ct. 
sary to briefly consider the arrangements which are found in 
one of the higher fern-like plants, Selaginella, a straggling 
form commonly found in greenhouses (fig. 65). The stem of 
the sporophyte is weak and bears numerous small leaves. Fertile 
shoots are present by the leaves of which spores are borne, 
and such a shoot satisfies the definition which describes a flower 
as ‘fa shoot modified for spore- bearing.” In ferns the 
spores are all of one kind, but in selaginella they are of two 
