334 PRACTICAL BOTANY 



A period of dormancy after the embryo is formed would cause 

 the old megaspore and its contents (female gametophyte and 

 embryo) to look much like the seed of spermatophytes. 



306. Spermatophytes. The sporophyte of the seed plants 

 is a far better nutritive-working plant than those of any of 

 the preceding divisions. Not only has it better structures 

 for making food, but many structures and habits enable these 

 plants to store surplus food from more active through less 

 active periods, or from year to year. 



From an evolutionary point of view the seed marks the most 

 important advance in the spermatophytes. The seed is the 

 megasporangium (ovule) and the remaining part of the female 

 gametophyte and the embryo sporophyte. It can lie dormant 

 through unfavorable periods, often for years, and upon return 

 of favorable conditions proceed to grow. Its stored food 

 nourishes the young plant until it establishes its own food- 

 making structures. 



In gymnosperms the megasporangium (ovule) and the seed 

 which is developed from it are borne upon the megasporophyll 

 and not within it, as in angiosperms. In the first case the 

 microspore (pollen grain) alights upon the ovule. A pollen 

 tube carries the male cells or sperms to the egg. In angio- 

 sperms the pollen grain alights upon the stigma of the carpel. 

 The pollen tube carries the male cells through the style to the 

 ovule, thence through it to the egg. In the gymnosperms the 

 female gametophyte is developed from the megaspore entirely 

 within the ovule, is composed of many cells compactly arranged, 

 and bears archegonia and eggs. In the angiosperms the female 

 gametophyte is not compact, is reduced to seven cells, and 

 bears an egg without a surrounding archegonium. Further- 

 more, this angiosperm gametophyte has a second period of 

 growth, which results in production of the endosperm of 

 the seed. 



In spermatophytes the gametophytes are very nearly lost. They 

 are so inconspicuous that they are hard to understand, but they 

 cannot be wholly lost while plants have sexual reproduction. 



