6 BIOLOGICAL LECTURES. 



without losing their vitality, thus answering physiologically to 

 the single oospore of the algae. In short, the resting period is 

 here shortened, owing to the power of the gametophyte to grow 

 on land, and for the protection of the growing sporophyte within 

 the archegonium. 



It must be remembered, however, that for fertilization to be 

 effected, the gametophyte must be covered with water, or, as it 

 were, go back to the original aquatic condition, since in all 

 Archegoniates water is necessary for the opening of the sexual 

 organs, as well as for conveying the ciliated spermatozoids to 

 the archegonium. 



This amphibious habit of the gametophyte is retained 

 throughout the whole group of Archegoniates, and is even 

 found in the lowest seed plants, e.g., Cycas. 



As the archegoniate type becomes better developed, we find 

 a change taking place in the relative importance of gameto- 

 phyte and sporophyte. While in certain groups like the leafy 

 liverworts and the true mosses there is a considerable amount 

 of specialization in the gametophyte, in other types, especially 

 those which seem to lead up to the ferns, the gametophyte 

 is much simpler in structure, and it is the sporophyte which 

 becomes the conspicuous phase. We must remember, how- 

 ever, that in these forms the sexual organs, archegonium and 

 antheridium, are essentially the same as in the lower liverworts 

 and true mosses, and like them require water in order that fer- 

 tilization may occur. 



As every botanist knows, the fern spore on germination pro- 

 duces, not the fern as we ordinarily understand it, but the 

 inconspicuous liverwort-like gametophyte, or " prothallium," 

 which not only closely resembles in general appearance a 

 simple liverwort, but also bears reproductive organs of very 

 similar structure. 



The change in the relative importance of gametophyte and 

 sporophyte has evidently been a very gradual one and is well 

 illustrated in the existing Archegoniates. 



It is safe to assume that the most primitive Archegoniates 

 had a sporophyte in which all the cells were sporogenous as 

 they are in Coleochaete, but no such primitive forms are known 



