RECENT WORK ON MOSSES AND FERNS. 371 



Pteridophytes ( Tmcsiptcris, Dancea, Ophioglossum) ; that 

 potential sporogenous tissue is converted into sterile tissue 

 (trabecular of Isoetes), and conversely tissue of a septum 

 may become sporogenous (abnormal Tmesipteris). From 

 these facts we conclude that the limits between sterile and 

 fertile tissue are not absolutely fixed, but that the two are 

 mutually convertible ; further, there is good reason to believe 

 that a progressive sept at ion has played a part in the pro- 

 duction of the numerous sporangia of Pteridophyta : how 

 prominent a part it has played must still remain an open 

 question. 



The admission of the process of septation as a probable 

 factor opens the way for fresh views of relationship. Dur- 

 ing the last quarter of a century various writers have noted 

 the similarity in position of the fertile spike of Ophioglossum, 

 and the sporangium of Lycopods : if the latter underwent 

 septation, a body something like the former would be the 

 result. The development has now been found to coun- 

 tenance such a view, while on a wide ground of comparison, 

 morphological, histological, comparison of the gametophyte 

 and embryology (as far as known), it appears that the view 

 is supported. It would not be advisable, however, to 

 carry such speculations further at present, and it must 

 constantly be remembered that other factors exist. It is 

 probable that fusion of sporangia may have occurred in 

 certain cases as exemplified by the ovales of Loranthus : it 

 is possible that there may have been in some cases a return 

 to the faculty of spore-production in parts which had pre- 

 viously been vegetative. It must remain for future investi- 

 gation to decide how far these various factors or others 

 may have been active in producing the numerous sporangia 

 of Pteridophytes as we see them. 



But the second great point of difference between Bryo- 

 phytes and Pteridophytes lies in the absence or presence of 

 appendicular organs. No one can fail to recognise the 

 enormous advantage which accrues from them ; they first 

 made physiological independence of the neutral generation 

 possible by providing for successful assimilation, fixture in 

 the soil, and more ready dispersal of the spores when 



