DEVELOPMENT OF PLANTS 335 



gametophyte. We see that the gametophyte is becoming para- 

 sitic upon the sporophyte (see page 265). After the spores are 

 shed they complete the growth of the gametophyte by forming 

 the archegonia and filHng the space within the spores with a soHd 

 mass of cells. This growth ruptures the spore walls at the apical 

 regions, thus exposing the archegonia to the male gametes (Fig. 

 243, 3). The archegonia are rudimentary structures consisting 

 of but two neck cells, and a single canal cell leads to the female 

 gamete. 



It is evident that these variations are of great advantage in 

 ensuring the perpetuation . of the species. Especially is the 

 nourishment of the young gametophyte by the highly organized 

 sporophyte a distinct gain. In previous types the formation of 

 the gametophyte was dependent upon favorable conditions, such 

 as moisture, light, temperature, etc., and it should be said that 

 only in rare cases do the spores fall in such favorable situations 

 and meet with such suitable conditions as to enable them to ma- 

 ture archegonia and antheridia, and so provide for a new sporo- 

 phyte. In Selaginella the formation of the gametophyte is en- 

 sured by the food supplied to it by the sporophyte. Thus the 

 germination of the spore is practically independent of its sur- 

 roundings and it can complete its growth under a variety of condi- 

 tions, even in the dark. It should also be noted that this relation- 

 ship of the two generations results in a marked reduction in the 

 size of both the male and female gametophyte, since they are no 

 longer burdened with the work of food construction. This re- 

 duction will proceed very rapidly as we advance through the 

 remaining groups. 



(c) Germination of the Gametospore. — The germination of the 

 gametospore is very much like that of the Lycopodium . The 

 suspensor is much longer and the young sporophyte consists of 

 a stem bearing two cotyledons, a well-developed foot and a root 

 that is developed after the other organs (Fig. 243, 3). The foot 

 continues to absorb food from the gametophyte after the stem 

 and root have emerged, and in this condition the relation of the 

 sporophyte to the gametophyte is strikingly suggestive of a 

 sprouting seed (Fig. 243, 4). In this connection it should be 



