STUDIES OF SPORE-PLANTS 243 



adapted to the light-relation, and this delicate side is protected 

 during drought by rolling of the edges of the leaf. 



232. Reproduction of Mosses. Many creeping branches 

 form rootlets, and after decay of the older stem may become 

 independent. This is the chief cause of the mats of mosses 

 often found. But in addition to this vegetative propagation, 

 all mosses reproduce by means of sex-cells and by spores. 

 Sex-organs (ovaries and spermaries) are formed in the bud- 

 like apex of the stem or of the main branches. Both kinds of 

 sex-organs are in some species found on the same plant (i.e., 

 it is monoecious) ; but in other species on separate plants 

 (dioecious}. A spermary (botanists usually call it an an- 

 theridium in mosses and ferns) is an elongated club-shaped 

 mass of cells (Fig. 73, E), the inner ones of which become con- 

 verted into swimming sperm-cells, which are freed by rupture 

 of the wall of the spermary. An ovary (usually called arche- 

 gonium, as in ferns) has the shape of a chemist's flask with 

 a long tubular neck (Fig. 73, F). In the rounded base of the 

 ovary is an egg-cell or ovum. This is fertilized by a sperm- 

 cell which swims down the neck of the ovary. The fertilized 

 egg-cell (or oosperm) divides into two, four, eight, and more 

 cells, forming the embryo. This soon begins to grow upward 

 as a slender rod, and the end of the rod expands into and 

 forms a vase-like structure (Fig. 73, C). This is a spore-case, 

 usually called by botanists the sporangium, and its inner 

 ceils form numerous spores. It usually has a cap-like lid, 

 which falls off when the spores are ripe and ready for scat- 

 tering. The entire stalk and spore-case formed from the 

 developing egg-cell is called sporogonium. 



When a moss spore begins to germinate, a delicate thread or 

 filament grows out and branches. This structure formed 

 by the germinating spore is called a protonema (meaning the 

 first thread). 



After a time one or more buds appear on the sides of this 

 protonema, and from them moss plants grow upward. Thus 



