8 BIOLOGICAL LECTURES. 



thickened elaters, whose principal function is to help in dis- 

 tributing the spores. 



While the last-mentioned type of sporophyte is character- 

 istic of most liverworts, there is one order sometimes con- 

 sidered to be a class, intermediate between the liverworts and 

 Pteridophytes, or ferns. In these Anthocerotaceae, of which 

 the genus Anthoceros is the most highly developed, the sporo- 

 phyte becomes far better developed than in any of the typi- 

 cal liverworts, although the gametophyte is exceedingly simple. 

 In these plants the sporophyte (Fig. 4, a) becomes relatively 

 very large, and is remarkable for the subordination of spore 

 production to the vegetative life of the sporophyte. The 

 sporogenous tissue is reduced to a single layer of cells at 

 least in the beginning. Outside of this sporogenous layer 

 are several layers of green cells with large air spaces between 

 them, which communicate with the outside atmosphere by 

 means of stomata precisely like those on the leaves of the 

 higher plants. There is no question that the spongy green 

 tissue forms a very efficient assimilative apparatus, like the 

 green tissue of ordinary leaves, so that the sporophyte is 

 probably quite able to provide its supply of carbon from the 

 atmosphere. The axial strand of cells, the columella (col.), 

 corresponds in position to the young vascular bundle in the 

 fern sporophyte, and possibly may, like it, serve as a means of 

 conducting water. No root is developed, however, and the 

 sporophyte must get its supply of water from the gametophyte 

 by means of the very large foot. 



Unlike all other liverworts, the sporophyte in the Anthocero- 

 taceae develops a zone of growing cells between the foot and 

 the upper part of the sporophyte ; and these active cells keep 

 adding new tissue to the base of the sporophyte, which may 

 thus continue to grow for several months. Were the sporo- 

 phyte connected with the earth by a root, it would be entirely 

 able to take care of itself and be quite independent of the 

 gametophyte. 



In tracing the evolution of the sporophyte in the Bryo- 

 phytes, or mosses, the most marked characteristic is the gradual 

 reduction of the sporogenous tissue, and its subordination to 



