402 THE NON-VASCULAR PLANTS 



may recall (see page 268) that we have defined a generation 

 as an individual which arises from a single cell. The spore 

 of a liverwort is, of course, a single cell. It gives rise to 

 the liverwort plant. That is one generation. The liver- 

 wort plant produces sperms and eggs (gametes) and a 

 fertilized egg or oospore results ; the oospore is a single 

 cell and it produces a structure called a sporogonium. The 

 sporogonium is therefore another generation. We may 

 illustrate this by a diagram in which large P stands for the 

 plant and large S stands for the sporogonium. 



PZ^gs m > °8spore S SP°" P 



All this would not be very important if it were a thing 

 which is true for liverworts alone. But it is not true of 

 liverworts alone. It is true of them and also true of all 

 the higher plants. Ferns and seed plants, as well as liver- 

 worts and mosses, all have alternation of generations. 

 We are explaining it now for them as well as for liverworts. 

 It is a thing which it is important for you to understand. 



Since two distinct generations occur in all the higher 

 plants, it is desirable to have names by which they may be 

 distinguished whatever their forms may be. Whatever 

 their form may be, these generations are always alike in the 

 reproductive cells which they produce ; that is, one genera- 

 tion always produces spores, the other always produces gam- 

 etes. The generation which produces spores is called the 

 sporophyte; the one which produces gametes is called the 

 gametophyte. Another way of stating the difference be- 

 tween these two generations is to say that sporophytes 

 always come from fertilized eggs, while gametophytes 

 always come from spores. In liverworts the plant is the 

 gametophyte and the sporogonium is the sporophyte. 



