BO REPRODUCTION 



letters, we may describe such an alternation in this way: 

 An individual A reproduces non-sexually, and when the 

 offspring become mature they are not As, but Bs. B, when 

 mature, develops gametes which unite, and the fertilized 

 eggs develop into organisms that are not like their parent 

 B, but like the grandparent A. A by budding or spore- 

 formation produces B; B, in turn, by sexual union, 

 produces A. 



3. The Moss and Fern Illustrate this Alternation. 



What has been described in the preceding section is 

 exactly the thing that happens in the mosses and ferns. 

 The small prothallium in the fern, which has been called 

 the gametophyte, has the two kinds of gametes. These 

 unite, start a new plant, which is the large fern plant that 

 grows to be very different from the little microscopic 

 prothallium. This large plant is the sporophyte generation. 

 It has a period of growth, and when it becomes mature it 

 cannot in any way produce eggs and sperms, but produces 

 great numbers of spores without any sexual union 

 whatever. We have seen that these spores germinate into 

 the gametophyte. The sporophyte is one generation and 

 the gametophyte is another. These generations regularly 

 alternate. 



In the moss we have exactly the same facts and in the 

 same order. In the fern both generations live independent 

 lives and the sporophyte is the better developed generation. 

 In the moss the gametophyte is the more important 

 generation and the sporophyte is parasitic on it. One 

 question about the moss may very properly be raised by 

 the student at this point. How do we know that the 

 structure that bears the spores in the moss is really a new 

 generation and not merely a part of the regular moss 

 plant, as it looks to be? That it is a new generation is 

 shown by the fact that it is produced by the development 

 of a fertilized egg. We know always that a new generation 

 begins when we start with a fertilized egg. 



