ioo Plant Life and Evolution 



which are absent from the embryo of the liverworts. 

 There is soon formed an outgrowth which breaks 

 through the overlying tissues of the gametophyte 

 and expands itself in the light as a little fan-shaped 

 green leaf. Another outgrowth pushes downward 

 and penetrates the soil and forms the primary root, 

 while a third structure becomes the permanent grow- 

 ing point, or stem apex of the little sporophyte, 

 which is now recognizable as the young fern (Fig. 

 n, A). During its early development, the little 

 sporophyte draws its nourishment from the game- 

 tophyte by means of a foot quite like that found in 

 the mosses and liverworts, but so soon as the first 

 leaf is expanded, and the primary root has pene- 

 trated the earth, the young sporophyte becomes an 

 independent plant. 



In the ferns the development of spores is often 

 delayed for many years, the sporophyte in the mean- 

 time increasing in size and developing special organs 

 and tissues which characterize these " vascular " 

 plants. The young sporophyte soon shows a definite 

 axis or stem, which usually possesses a permanent 

 growing point, from which arise later on many 

 leaves and roots. An extensive system of conduct- 

 ing tissue is a characteristic of the sporophyte of the 

 ferns, which are called sometimes for this reason 

 " vascular cryptogams." This " fibro-vascular " 

 system constitutes a tissue especially modified for 

 water conduction and for the transport of food sub- 

 stances. While similar tissues, as we have seen, may 



