56 PLANT-LIFE ON LAND [CH. 



the middle of the 19th century, views of descent 

 began to make their influence felt upon the study of 

 form in plants. But it was only slowly that this 

 became apparent in a fuller knowledge of the genesis 

 of the flower of the higher plants. Consequently it 

 has only been in recent decades that the acceptance 

 of the flower as the result of metamorphosis of a 

 vegetative shoot has ceased to satisfy. It will be 

 well to explain the reasons for the change. 



In a previous chapter (p. 44) it has been shown 

 that the life-story of a Fern consists of two phases, 

 the relatively small green prothallus and the relatively 

 large spore-bearing Fern plant. It was Hofmeister 

 who first recognised that a similar alternation of two 

 such phases is characteristic of all Vascular plants, 

 including all those which bear flowers. In all of them 

 that obvious thing which we call " the Plant ' is the 

 spore-bearing generation, and its end is the forma- 

 tion of sporangia and spores. What we are now 

 considering is the evolutionary relation of the sterile 

 and fertile regions of such plants. 



In every normally completed life of Vascular plants 

 sporangia are formed. This is so in all living Ferns, 

 Club-Mosses, and Horsetails, as well as in Seed-bear- 

 ing plants. Moreover the evidence of the fossils 

 shows that it was the same with the related plants of 

 the distant past. Hence we may conclude that it has 

 been so throughout their descent. If this be true, 



