280 SCIENCE PROGRESS. 



presence of an axial mass of tissue (columella) which both 

 morphologically and physiologically is probably to be 

 directly compared to the vascular bundles of the higher 

 plants. In the sporophyte (sporogonium) of these higher 

 Muscineae, only a very small amount of tissue is devoted to 

 the production of spores, in strong contrast to the lower 

 Hepaticae where practically the whole sporogonium is com- 

 posed of sporogenous cells. 



While in a general way it may be said that the evolution 

 of gametophyte and sporophyte in the Muscineae is parallel,, 

 this is by no means always the case. Thus Antkoceros,. 

 whose sporophyte comes the nearest to an absolutely in- 

 dependent condition of any Bryophyte, has the gametophyte 

 of an exceedingly simple type. In this genus, the sporo- 

 phyte not only possesses an elaborate assimilative system 

 and a central conducting tissue, but its growth is not 

 stopped by the formation of spores, but continues as long as 

 the gametophyte remains alive. 



In the Ferns the development of the sporophyte is 

 carried still further, and by the production of a special 

 organ, the root, it becomes entirely self-supporting and 

 sooner or later the gametophyte dies. The sporophyte of 

 the Fern at first sight shows little in common with the 

 sporogonium of the most highly organised Moss, but a. 

 more careful scrutiny shows that the differences are less 

 than appears at first. The great difference consists in the 

 development of special organs, leaf, root, stem, sporangia,, 

 in the former, while the compact bryophytic sporogonium 

 in no case shows any such external differentiation. 



On comparing the gametophyte of the Pteridophytes 

 with that of the Muscineae we find that it resembles in most 

 cases the simpler Hepaticae rather than the more specialised. 

 Mosses ; and in the case of most Ferns this resemblance is 

 extraordinarily close. The earlier observers noticed the 

 very obvious resemblance of a Fern prothallium to a thallose- 

 Liverwort, and concluded that here was the point of con- 

 tact between the two series of the Archegoniatae. When, 

 however, an attempt was made to homologise the sporo- 

 gonium of any known Bryophyte with the Fern plant, the 



