x] GENERAL OUTLOOK 159 



influence is restricted by the limits of the water- 

 medium within which it acts (Chapter III). Thus 

 what may be styled the primary vegetation of the 

 Land, including Mosses and Ferns and their allies, 

 constituted a true Land Flora as regards their 

 vegetative system, but their propagative method 

 was conservative and ineffectual for land -living plants. 

 It remained typical of their aquatic ancestry, and 

 suffered from natural restrictions on dry land. Such 

 a Flora might be styled in a sense amphibial. 



It remained for the Seed-plants to break loose 

 from these limitations, and to become a Land Flora 

 in the full sense of the term. The most important 

 change which they show is in the method of their 

 fertilisation by the pollen-tube. The pollen-grains 

 can be transferred from the stamen to the stigma 

 at any time, and dry conditions will even favour the 

 process, while the further growth of the pollen-tube 

 down the style is independent of external fluid water. 

 Thus the conservative restriction which hampered 

 the primary vegetation of the Land was finally 

 removed It has been seen that the Mosses and 

 Ferns and their allies are deficient in opportunity 

 for intercrossing, as a consequence of their aquatic 

 method of fertilisation. This disability also falls 

 away in the Seed-plants. They show as one of 

 their most popular and sensational features an 

 extraordinary facility in the use of external agencies 



