CAL AMITE S 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. — Selaginella 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; /, 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- 



