[Chap. L THE SEED PLANTS 691 



number of chromosomes in each nucleus, whereas each cell of the sporo- 

 phyte has the diploid number of chromosomes. 



7. Monoploid and diploid numbers of chromosomes are not causes 

 of the two phases in the life cycle, but are merely associated with them. 

 Doubling or other multiplication of the number of chromosomes neither 

 changes the phase nor necessarily prevents the alternation of phases. 



8. The conspicuous phase of many algae, the liverworts, and the 

 mosses is the gametophyte; the conspicuous phase of brown algae, the 

 ferns, and seed plants is the sporophyte. 



9. The sporophytes of the liverworts and of the mosses are partial 

 parasites on the gametophytes. 



10. Both the gametophytes and sporophytes of ferns develop as sep- 

 arate green plants. 



11. The gametophytes of seed plants are parasitic on the sporophytes. 



12. Some ferns, some club mosses, and all seed plants have two kinds 

 of spores: microspores and megaspores. 



13. Two distinct gametophytes develop from these spores. From the 

 germination of microspores there result gametophytes in which sperms 

 only are formed; and from the germination of megaspores there result 

 gametophytes in which egg cells only are formed. The size of the spore, 

 however, is not a cause of the difference in development of the two 

 gametophytes. 



14. In the equisetums the spores are physiologically unlike but sim- 

 ilar in appearance. From half of them antheridial gametophytes de- 

 velop, and from the other half archegonial gametophytes result in cer- 

 tain habitats. 



15. In ferns, club mosses, and equisetums the two kinds of spores 

 germinate on the soil after falling from the parent sporophyte. 



16. A megaspore of Selaginella occasionally germinates in the mega- 

 sporangium, resulting in an enclosed gametophyte with archegonia and 

 egg cells. The germination of the fertilized egg may result in the de- 

 velopment of an embryo within this sporangium, and the final result is 

 a seed. If the megaspore falls to the ground and germinates there, no 

 seed results. 



17. In seed plants the germination of the megaspore occurs within 

 the ovule ( megasporangium ) , and this is a first step in a series of proc- 

 esses that results in the formation of a seed. 



18. Seeds of flowering plants consist of seed coats, endosperm, and 

 embryo; or only of seed coats and embryo. 



