340 PRACTICAL COURSE IN BOTANY 



bears the gametes, or sexual organs, — the suffix phyte mean- 

 ing a plant ; for example, epiphyte, on or upon plants ; spermo- 

 phyte, or spermatophyte, seed plant ; sporophyte, spore plant. 

 The sporophyte, produced within the archegonium, bears 

 simple nonsexual spores that are capable of germinating 

 independently. Structurally it is a separate, individual 

 organism, though it does not appear as such in this class, 

 but lives inclosed in the archegonium, as a parasite on the 

 mother plant. 



395. Alternation of generations. — If we represent the 

 sporophyte by >S^, the thallus, or gametophyte, by G, the 

 female gamete, or egg cell, by fg, the antherozoids (male 

 gametes) by 7ng, the fertilized egg cell, or oospore, result- 

 ing from their union by oos, and the asexual spores dis- 

 charged from the sporophyte by 0, this complicated mode 

 of reproduction may be expressed diagrammatically as 

 follows : — 



'^<C ^>ods-* S ». ^(^^<r "> oos -^S — > vG^etc. 



A glance at the diagram will show a continual inter- 

 change of the sexual and asexual modes of reproduction, in 

 which each generation gives rise to its opposite, the asexual 

 sporophyte producing the sexual gametophyte, and this in 

 turn, through its gametes, giving rise to the asexual sporo- 

 phyte. This regular recurrence in genealogical succession of 

 two differing forms is what is meant by the expression " alter- 

 nation of generations." Analogous processes occur also 

 among some of the thallophytes, but as there is no well- 

 defined differentiation of sporophyte and gametophyte, 

 alternation proper may be regarded as beginning with the 

 bryophytes. The subject is a complicated one and some- 

 what difficult to grasp, but it is important to form a correct 

 idea of it and to fix clearly in mind the different modes of 

 reproduction as we proceed from the lower to the higher forms 

 of vegetation, since in this way alone can their biological 



