DEVELOPMENT OF PLANTS 351 



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

 and meet with such suitable conditions as to enable them to 

 mature 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 Lycopodium. The sus- 

 pensor 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 

 remembered that the young sporophyte of certain species remains 

 in the gametophyte during the winter or during a drought in a 

 resting or dormant condition, thus resembling very closely the 

 seed structure to be seen in the next group. It may also be 

 stated that fertilization and even the formation of the young 

 sporophyte may begin before the spores are discharged from the 

 sporangium, thus helping us to understand how it came about 

 that the megaspores were permanently retained in the sporan- 

 gium as is the case among seed plants. In one of the large 

 groups of Pteridophyta that have become extinct, it is note- 

 worthy that both the gametophyte and young sporophyte were 

 retained in the sporangium so that the seed-like structures were 

 formed. 



