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. 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; 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, calami tes, 

 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- 



