1 6 THE BIOLOGY OF THE SEA-SHORE 



evolved and gradually increased in complexity till at length 

 unicellular plants were produced possessing chlorophyll, 

 and capable of elaborating their own food. At this period 

 portions of the earth's crust were uplifted to within a com- 

 paratively short distance of the surface of the ocean, and 

 came within the influence of the sun's rays. Profiting by 

 the presence of light some of the pelagic forms took to a 

 sedentary life upon the sea-floor, and from these were evolved 

 multicellular forms of gradually increasing complexity 

 and with more and more efficient forms of attachment. 

 Next, at a period corresponding to the very earliest geological 

 record, the earth's crust underwent a further movement 

 of uplift and areas of solid land appeared above the surface 

 of the waters. Certain sedentary aquatic plants now found 

 themselves exposed at intervals to the air. As the uplift 

 continued the periods of emergence became gradually longer ; 

 some of the sea forms again were able to adjust themselves 

 to the changing conditions, their organs of attachment 

 becoming organs of absorption, and reproductive cells 

 capable of aerial dispersal taking the place of those adapted 

 for locomotion or transport in water. Such was the way 

 in which, according to Church, plant life proceeded to its 

 conquest of the land. It will be seen that although this 

 writer assigns a pelagic origin to life, yet his theory emphasises 

 the importance of littoral conditions without which the 

 migration from sea to land would not have been possible. 



Totally opposed to that of Church is the view taken by 

 Osborn (191 8), who argues that the more or less complete 

 absence from the primal ocean of those chemical elements 

 so essential to living matter (particularly nitrogen) must 

 force us to abandon the idea of life having begun in the 

 sea and to conclude instead that " the lowliest organisms 

 originated either in moist earths or in those terrestrial 

 waters which contained nitrogen." Nitrite and nitrate 

 presumably arose by the union of nitrogen and oxygen in 

 electrical discharges (as in a thunderstorm) and with related 

 nitrogen compounds " may have been specially concen- 

 trated in pools of water to degrees particularly favourable for 



