INTRODUCTION 3 
fluid water at this critical period: it may thus be held to have broken 
away from a condition of life inconvenient and embarrassing to organisms 
which live on exposed land-surfaces: and to have established itself in 
this character, as well as in its vegetative development, as a typical 
land-living organism. If this view of the matter be adopted, it follows 
that the Mosses and Ferns occupy a middle position in the relation to 
water: they may almost be described as amphibious, since, though they 
vegetate mostly on land, and show certain advanced structural adaptations 
to such life, they are nevertheless dependent upon external water for the 
important incident of fertilisation in each individual life-cycle. The 
strange feature is that they have retained so persistently this aquatic 
type of fertilisation. 
Looking further down in the scale of vegetation, attention is naturally 
directed towards the Algae, plants resembling, in some superficial 
characters of cell-structure and of colouring, the simpler terms of the 
Archegoniate series, though still more dependent than they upon external 
fluid water for the completion of their life-cycle. It may well be that 
the affinity which such features suggest is at best only a remote one; 
but at least the existence of such forms would seem to justify the view 
as a probable one, that the great Archegoniate series, which has had 
so large a share in initiating that Land-Flora which we now see occupying 
the exposed land surfaces of the globe, has had its origin in aquatic 
forms: that from these a gradual adaptation to a land-habit has provided 
those forms of vegetation which we group together under the terms, 
Liverworts, Mosses, Club-mosses, Horsetails, and Ferns: and_ finally, 
with further adaptation to the land-habit, came the Seed-Plants—first 
the Gymnosperms and subsequently the higher Flowering Plants. The 
latter culminated in the Gamopetalous Dicotyledons, which are essentially 
of Flowering Plants the most typical elements of a Land-Flora, since 
they include a smaller proportion of aquatic species than either the 
Monocotyledons or the Archichlamydeae. 
This, then, is the general position adopted at the outset: it is in 
accordance with the known facts of Palaeontology, and is the view 
generally entertained by modern morphologists. It will be the object of 
the present work to enquire into the details of such progressions as 
those above mentioned; especially it will be our duty to see how far 
the life-histories of Archegoniate forms will justify the view that the 
present Land-Flora has originated from an aquatic ancestry, and that 
there has been a migration from the water to the land: in that case, 
it will be a further object to ascertain how this has been carried out, 
and to trace those methods of specialisation to a land-habit, which 
have led to the establishment of the higher terms of the series as the 
characteristic representatives of the Flora of exposed land-surfaces. 
It is no new view which is thus to be put forward; for it has long 
ago been concluded that the origin of life, whether animal or vegetable, 
