The Story of Evolution 65 



and work ; and the entire system of animate nature depends upon 

 the photosynthesis that goes on in green plants. 



As the result of much more explosive life, animals have to 

 deal with much in the way of nitrogenous waste products, the 

 ashes of the living fire, but these are usually got rid of very 

 effectively, e.g. in the kidney filters, and do not clog the system 

 by being deposited as crystals and the like, as happens in plants. 

 Sluggish animals like sea-squirts which have no kidneys are 

 exceptions that prove the rule, and it need hardly be said that 

 the statements that have been made in regard to the contrasts 

 between plants and animals are general statements. There is 

 often a good deal of the plant about the animal, as in sedentary 

 sponges, zoophytes, corals, and sea-squirts, and there is often a 

 little of the animal about the plant, as we see in the movements of 

 all shoots and roots and leaves, and occasionally in the parts of 

 the flower. But the important fact is that on the early forking of 

 the genealogical tree, i.e. the divergence of plants and animals, 

 there depended and depends all the higher life of the animal 

 kingdom, not to speak of mankind. The continuance of civilisa- 

 tion, the upkeep of the human and animal population of the 

 globe, and even the supply of oxygen to the air we breathe, 

 depend on the silent laboratories of the green leaves, which are 

 able with the help of the sunlight to use carbonic acid, water, and 

 salts to build up the bread of life. 



2 



The Beginnings of Land Plants 



It is highly probable that for long ages the waters covered 

 the earth, and that all the primeval vegetation consisted of simple 

 Flagellates in the universal Open Sea. But contraction of the 

 earth's crust brought about elevations and depressions of the 

 sea-floor, and in places the solid substratum was brought near 

 enough the surface to allow the floating plants to begin to settle 

 down without getting out of the light. This is how Professor 



VOL. 15 



