FUNDAMENTAL PRINCIPLES l8l 



to apply to the resulting diploid organism through all 

 stages of its development to maturity. 



165. Two Kinds of Generivtions. — A study of the life 

 history of the fern disclosed two distinct phases or genera- 

 tions, one bearing spores, and therefore called the sporo- 

 phyte (spore-bearing plant) , the other bearing gametes and 

 for that reason called the gametophyte (gamete-bearing 

 plant). The gametophyte of the fern was seen to be 

 entirely independent of the sporophyte, capable of manu- 

 facturing its own food by means of its own chlorophyll, 

 not dependent upon any other plant, and in some groups 

 being perennial, living on from year to year, and giving 

 rise to sporophytes that live for only one season. The 

 sporophyte, on the other hand, is at first, entirely de- 

 pendent upon the gametophyte for its nutrition, living as 

 a parasite upon the prothallus, from which it absorbs its 

 nourishment by means of the special organ, the foot. 

 Gradually, however, the sporophyte puts forth roots, 

 capable of taking in water and dissolved mineral sub- 

 stances from the soil, and chlorophyll-bearing organs (the 

 fronds or leaves), capable of manufacturing organic food. 

 As the sporophyte becomes independent, the gameto- 

 phyte (with few exceptions, as noted above), perishes. 

 A comparison of the two generations shows that the 

 sporophyte is the much more complex of the two, being 

 clearly differentiated into roots, and leafy shoot. The 

 difference in the origin of these two generations results in 

 a very fundamental difference in the nature of all the 

 cells in each. Since the sporophyte is derived from an 

 oosperm (zygote), formed by the fusion of the two 

 gametes, all of its cells are diploid, containing material 

 derived from both its male and female parentage. The 



