lxviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. lxxix,. 



or with methods of guarding against excessive loss of water by 

 evaporation from its leaves. In a plant rooted in the ground 

 absoi-ption is localized, provision must be made for an ascending 

 water-current and for the regulation of transpiration. The life- 

 history as also the structure of a plant are affected by the- 

 nature of the environment. The majority of biologists probably 

 believe that life began in the sea : it is easier for many of us to- 

 picture the birth in the sea of living organisms capable of building 

 up their substance from carbon-dioxide gas and mineral salts under 

 the influence of solar energy, than to imagine a similar act of 

 creation on land or in a freshwater lake. Assuming the first 

 scene to have been enacted in the ocean, what were the events 

 which led to the subsequent evolution of the pioneers of a land- 

 vegetation ? It would be out of place to discuss the various 

 hypotheses which have been advanced, but I cannot refrain from a 

 brief reference to an ingenious and able attempt recently made bv 

 Dr. A. H. Church, of Oxford, to follow the steps of the great 

 migration of the vegetation of the ocean to the surface of the land. 

 He regards as untenable the view that it was from simple freshwater 

 Alga?, which had wandered from their original home in the sea, that 

 the earliest land-plants were derived. Dr. Church sees the birth of 

 free-floating unicellular plants in the waters of a world-ocean. At 

 a later stage, when the uplifting of portions of the earth's crust 

 raised the ocean-floor within range of the sun's rays, the floating 

 plants were able to attach themselves to the solid substratum, and 

 a further step was taken in the elaboration of the plant-body. A 

 Plankton phase of floating life was followed by a Benthic phase, 

 when a sedentary existence favoured the evolution of a relatively 

 complex type of construction. When portions of the crust 

 emerged above the water, the submarine vegetation was faced with 

 fresh problems consequent on the change from water to aiiv 

 Power to live under the new conditions could only be gained by 

 drastic structural changes : the plants which solved the problem 

 were the advance-guard of the vegetation of the land. The 

 assumption of the existence of an ocean which completely enveloped 

 the earth before the beginning of the geological record presents 

 many difficulties ; on the other hand, as Prof. A. S. Eddino-ton 

 recently stated, a world-ocean is not inconceivable to an astronomer. 

 But, although Dr. Church postulated a world completely covered 

 by water, I venture to think that the stages in the evolution of a 

 terrestrial vegetation which he describes do not demand such an 



