710 CONCLUSION 



Bryophyta may be dismissed as side issues, and the special phyletic 

 interest will centre round the vascular Archegoniatae, as the forerunners 

 of all the higher vegetation of the Land. 



The method above described may be first applied in the case of the 

 GAMETOPHYTE of the homosporous forms of Pteridophytes. A comparison 

 of the prothalli of various species of Lycopodium (pp. 340-345) points 

 towards a massive body, probably exposed above ground and capable 

 of assimilation, with its sexual organs sunk in the massive thallus : the 

 form seen in L. Selago is held to be not far removed from the original 

 type. Probably the filamentous condition seen in L. Phlegmaria is a 

 specially attenuated development in accordance with saprophytic habit, 

 while the colourless condition of the underground prothalli, where depend- 

 ence is entirely upon saprophytic nutrition, can hardly have been anything 

 else than secondary. The same opinion applies also for the prothalli of 

 the Ophioglossaceae as regards their colour, and the deeply sunken sexual 

 organs (p. 465), while their massive construction compares with that usual 

 in Lycopodium. The female prothallus of Equisetum is of essentially a 

 similar type, but it shows less massive structure, especially in the upward- 

 growing lobes, which are not unlike those of L, cernuum. The male 

 prothallus is, however, of a simpler type : the antheridia are sunk as 

 before, but the archegonial neck projects, as it does also in some species 

 of Lycopodium. Turning to the Ferns, the delicate prothallus of the 

 Leptosporangiates, and especially the simple filamentous forms of the 

 Hymenophyllaceae, suggests at first sight that they are of an essentially 

 different type from the more massive forms previously considered. But 

 comparison within the Fern-phylum shows that the prothallus of the most 

 ancient living type, the Marattiaceae, is more massive in construction : 

 and in the Osmundaceae the same is seen, though in less degree. These 

 facts strongly suggest that the Fern-phylum has undergone a progressive 

 simplification of the prothallus, and indicate an origin like the rest from 

 a massive source. The sexual organs also are deeply sunk in the Euspor- 

 angiate types, but show a successively more projecting position in the 

 Leptosporangiates, just as their sporangia also project more than in 

 Eusporangiate Ferns. Thus the propagative organs of the two generations 

 march parallel in respect of their relation to the surface of the part which 

 bears them. // may accordingly be concluded as probable that the prothallus 

 of early Pteridophytes at large was a relatively massive green structure, 

 with deeply sunk sexual organs. 



Turning now to the comparison of the SPOROPHYTE, the phylum of the 

 Lycopodiales, in which it is of the simplest construction among the 

 Pteridophyta, is certainly as ancient as any of the rest : the two constituent 

 series, the Ligulate and the Eligulate, illustrate parallel progressions, but 

 their similarity of plan shows that they are closely allied. On the basis 

 of comparison of the known forms a primitive type of Eligulate Lycopod 

 has been sketched out, and it is nearly approached by what is actually 



