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. 349-345) 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 Z. Se/ago is held to be not far removed from the original 
type. Probably the filamentous condition seen in Z. 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 Aguzsefum is of essentially a 
similar type, but it shows less massive structure, especially in the upward- 
growing lobes, which are not unlike those of JZ. 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. J¢ 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 
. 
