598 MOSSES AND FERNS chap. 



phytes, and in all probability is to be regarded as its homologue. 

 This central strand of conducting tissue, together with the 

 massive assimilative tissue system of the larger species of An- 

 thoceros, would make the sporogonium independent of the 

 gametophyte, were a root or some similar structure present by 

 which it could be connected with the earth. The alternation of 

 sporogenous and sterile cells in the archesporium, by which the 

 latter is divided into imperfect chambers containing the spores, 

 is, perhaps, the first indication of the separate sporangia of the 

 Pteridophytes. The most striking difference, then, between 

 the sporogonium of Anthoceros and the sporophyte of the sim- 

 pler Pteridophytes, such as Ophioglossum and Phylloglossum, 

 aside from the absence of roots, which are, physiologically, 

 replaced by the massive foot, is the absence of a definite axis 

 with its lateral appendages (leaves) and sporangia. In Antho- 

 ceros the assimilative tissue forms a uniform la3^er over the 

 whole upper portion of the sporophyte, instead of -being 

 restricted mainly to the special organs of assimilation or leaves, 

 and the archesporium is continuous instead of being divided 

 into definite sporangia. It has been claimed by Bower, how- 

 ever, that in Ophioglossum also there is originally a continuous 

 layer of sporogenous tissue, and the formation of the sporangia 

 is secondary. 



Many attempts have been made to explain the origin of the 

 leafy axis of the sporophyte of the vascular Archegoniates from 

 the Bryophyte sporogonium. The latest theory is that of Pro- 

 fessor Bower (i6), who has brought forward much important 

 evidence to show that the simpler strobiloid Pteridophytes, 

 especially Phylloglossum, are the primitive forms from which 

 the others have sprung. His conclusions are based largely 

 upon a comparison of Phylloglossum with the embryonic con- 

 dition of Lycopodhim, where the long dependence of the embryo 

 upon the prothallium, the rudimentary vascular bundles, and 

 the late appearance of the root are very striking, and certainly 

 indicate a very low rank for these forms in the pteridophytic 

 series. Another evidence of the close relation of the Lycopo- 

 dinese to the Bryophytes is the character of the spermatozoids, 

 which closely resemble those of the Liverworts, both in their 

 small size and the two cilia. Professor Bower's theory as to 

 the origin of the sporophytes is that these arose ''by a process 

 of eruption from a hitherto smooth surface." In this way 



