THE EVOLUTION OF THE SPOROPHYTE. 9 



the purely vegetative part of the sporophyte, which finally 

 approaches an independent condition, most evident in such 

 forms as Anthoceros and the true mosses. In these plants, 

 by the development of a special assimilative green tissue, com- 

 municating with the outside atmosphere by means of stomata, 

 the sporophyte becomes entirely independent, so far as its supply 

 of carbon is concerned, as it can utilize the CO2 of the atmos- 

 phere. It remains, however, to some degree dependent upon 



Fig. 4. — a, Diagram of a longitudinal section of the sporophyte of Anthoceros, the nearest 

 approach to the sporophyte of the ferns found among the Bryophytes. The sporogenous 

 tissue is confined to a single layer surrounding the central strand of tissue, or columella, 

 col. A large foot is developed, and the outer tissues develop chlorophyll. The tetrads of 

 spores are separated by sterile cells, st. b, Cross-section of the same, c, Diagram of a 

 vertical section of a young fern embryo showing its close resemblance to the correspond- 

 ing stage of the liverwort sporophyte. d, A similar section of an older fern sporophyte 

 showing the formation of the external organs — stem, 5. ; leaf, L. ; root, R. ; and foot, F. 

 •Each of these young organs contains an axial strand of elongated cells, the beginning of 

 the vascular bundle. 



the gametophyte, from which it secures water and some nitrog- 

 enous food materials, very much as a parasitic plant does from 

 its host. 



While the higher Bryophytes show considerable differentia- 

 tion in the sporophyte, so far as the tissues are concerned, 

 there is little or no external differentiation, and nothing com- 

 parable to the leaf and stem found in the sporophyte of the 

 higher plants. If, however, in such a form as Anthoceros, we 

 could imagine the large absorbent organ, the foot, to penetrate 



