THE ORIGIN OF THE VASCULAR PLANTS. 279 



as they undoubtedly are the connecting links between the 

 Flowering Plants and the simpler green Algae which most 

 botanists are agreed are allied to the progenitors of all the 

 higher plants. Just which of the modern forms are most 

 nearly allied to this ancestral type is not certain, but on the 

 whole the genus Coleochczte seems to show the greatest 

 resemblance to the simplest known Archegoniatae. 



It is the purpose of this paper to sketch briefly the 

 process, so far as we can trace it, by which the vascular 

 plants gradually developed from the lower Archegoniatae, 

 and to state the somewhat conflicting views held by different 

 botanists at the present time as to the relationships of the 

 principal groups of the Archegoniatae to each other, and 

 their connection with the Algae on the one hand, and the 

 Spermaphytes (Phanerogams) on the other. 



In all of the Archegoniatae there is a marked alternation 

 of sexual and non-sexual plants which are extremely different 

 from each other both in structure and development. In 

 the lower members of the series, the non-sexual generation 

 (Sporophyte) is insignificant, and physiologically is merely 

 a spore-fruit borne upon the sexual plant or gametophyte, 

 but in the higher ones it graduallv becomes more and more 

 an independent organism, and finally all connection with 

 the gametophyte is severed. 



The Archegoniatae are usually divided into two groups, 

 the Muscineae or Mosses in the widest sense, and 

 Pteridophyta or the Ferns and their allies. In the first 

 series the sporophyte never becomes entirely independent ; 

 in the second it always does. Within the first, however, 

 there is great difference in the degree of dependence of the 

 sporophyte. In the simplest ones, e.g., Riccia, the sporo- 

 phyte is simply a mass of spores surrounded by an im- 

 perfect layer of sterile cells. In all the others, however, 

 a greater or less amount of sterile tissue is developed, which 

 at first serves simply to nourish the growing spores, but in 

 the higher Mosses and Liverworts forms a true assimilative 

 tissue, with green parenchyma and stomata quite com- 

 parable to the assimilative tissue system of the vascular 

 plants. The resemblance is still further increased by the 



