336 ORIGIN OF THE SEED 



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 resembHng 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 noteworthy 

 that both the gametophyte and young sporophyte were retained 

 in the sporangium so that the seed-like structures were formed. 



