168 PLANT-LIFE 



tains several megaspores. The development of the 

 spores and the sexual generation, the gametophyte, is 

 much ,like that of Selaginella. The Isoetaceae, as we 

 have them to-day, seem to be survivors of an ancient 

 group of plants which was numerous in earlier geological 

 periods. The spermatozoids generated by the antheridia 

 are multiciliate, as in the case of the Ferns, and it is a 

 debatable point as to whether the Isoetaceae are not 

 more nearly related to the Ferns than to the Club Mosses, 

 with which they are usually grouped. 



We have now concluded our rapid resume of the 

 salient features of the Pteridophytes. The bald facts 

 that have been stated may not stand for much in the 

 mind of an unimaginative person, but to the intelligent 

 and thoughtful reader, who reads between the lines, they 

 will appear pregnant with suggestion, and will not fail 

 to arouse wonder and awe. For the facts represent the 

 patient and majestic progress of plant-life. All the 

 earliest plants were aquatic and of the simplest type. 

 Advanced aquatic plants have some complexity of struc- 

 ture, but it was in the invasion of the land and the deter- 

 mination to colonize it that greater complexity was 

 demanded. The Pteridophytes in their sexual genera- 

 tion, in which water is necessary for the progress of the 

 ciliated male elements and the act of fertilization, 

 betray their aquatic ancestry. In the development of a 

 Fern, we may say that we have evolution proceeding 

 before our eyes. The utter dependence of the asexual 

 generation upon the sexual in the Moss group does not 

 exist among the Ferns. In the Mosses the sexual 

 generation is " the plant "; but the asexual sporophyte 



