CALAMITES AND LYCOPODS 387 
recognized at once as a new feature in life history. By 
successive divisions the protoplasm of the spore becomes a 
multicellular body, the prothallus, with richer cells near the 
apex. Here a number of archegonia form (Fig. 283), and 
the enlargement of the prothallus, or gametophyte, causes 
a splitting apart of the old, thick walls of the megaspore, 
so that the female gametophyte protrudes (Fig. 284, 9). 
FIG. 283. Sclagindla Kraussiana. C, section of mature female gam- 
etophyte, showing three archegonia, two containing eggs, and one (at the 
left) an embryo with suspensor (sus.). D-G, Stages in the development 
the archegonium; H, very young embryo (two-celled stage), after first 
division of the fertilized egg; 7, older embryo (Em), with suspensor (s). 
(After Campbell.) 
It bears no chlorophyll, living entirely as a parasite on 
the parental sporophyte, from whence it derives all the food 
with which it nourishes the embryo. 
348. Fertilization. As throughout the ferns, calamites, 
and lycopods, fertilization is accomplished by the swimming 
of the sperm to the mouth of the archegonium, and down 
the neck-canal to the ripe egg in the venter. Thus while 
Selaginella is, in other respects, a land-plant, it retains 
the aquatic method of fertilization. External water is 
absolutely necessary in order that the sperm may reach 
the egg. 
349. The Embryo. After fertilization the oosperm 
begins to divide. The cell nearest the neck of the arche- 
