Evolution of Plants 345 



or lateral expanse of cells forms, that is the rudiment of the 

 sexual or gametophyte plant, and so corresponds to that of 

 Coleochcete scutata, of Riccia glauca, of Sphcerocarpus or the 

 leafy rudiment of a Phascuvi. As in Coleochcete ov Riccia 

 tliis soon may transform surface cells into antheridia and 

 archegonia, which scarcely differ even in minor details from 

 those of the latter genus except that condensation in the neck- 

 canal cells is observed. But the fertihzed egg gives rise to 

 a very different and greatly more complicated structure than 

 even the most elaborate sporophyte of the Hepaticte or Musci. 

 And it is in the absence, at the present day, and as yet also 

 from the palseontological record, of connecting stages in the 

 evolution of the sporophyte body or plant that the great gap 

 exists. 



It would lead us too far here to give even an abstract of the 

 varied views that have been advanced to account for the course 

 of morphological development taken. These have been re- 

 viewed by Lotzy (119, 2: 388) and others comparatively re- 

 cently. So a brief outline will alone be given of what seems 

 to the author to have been the probable course of events. 



AKke in th^ Hepaticse and Musci the sporophyte is a struc- 

 ture that grows into and absorbs all of its nourishment from 

 the sexual plants. Its entire function is to develop spores 

 within a more or less simple or complicated wall-cavity, the 

 sporangium. But, through cooperation of agencies, most of 

 which have already been named as environal factors, it as- 

 sumed an increasingly dominant size and complexity, so as 

 mechanically to press on and reduce in size the sexual genera- 

 tion, till this even in its early phases arose close to the ground. 

 Now through inability of the sexual generation to keep pace 

 with the nutritive needs of the sporophyte, in line however 

 with the growth-continuity relation of one to the other, as 

 well as unceasing environal action and proenvironal reaction 

 between each organism and its surroundings, absorptive and 

 elaborating structures, that each more or less closely simulated 

 those on the nutritive body of the sexual generation, grew 

 out of the sporophyte body. 



So the green cellular lobes, filaments, or flattened expanses 

 — that we now know various prothalHa amongst species of 



