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, 



