THE APPEARANCE OF LIFE 69 



Thus we see how the mere process of nutrition has sufficed 

 to decompose our hypothetical layer of living granules into 

 three strata : a green one corresponding to the algae, a colourless 

 one containing granules enveloped in cellulose corresponding 

 to the fungi, and one with free granules, corresponding 

 to the animals. 



The knowledge we possess to-day thus permits us to form a 

 logical idea of the conditions necessary for the appearance of 

 life, alike for the formation of the animal and vegetable 

 kingdoms, without presupposing the interference of anything 

 but ordinary chemical or physical phenomena, or appealing 

 to any but the simplest considerations — which to some people 

 may appear even too simple. Natural laws, however, are always 

 simple. It is only our mind that loves to surround itself with 

 mystery and complication. 



It may naturally be asked why those cells which do not form 

 chlorophyll when they are in the dark should not again develop 

 the power to do so when they are brought into contact with 

 light. But it is a general rule that a function which is not 

 exercised disappears, and the faculty of making chlorophyll 

 can disappear even in the higher parasitic plants like Monotropa, 

 the broom-rapes, and orchids of the genus Neottia, just as in 

 the underground roots of ordinary plants. 



One particularly tantalizing problem remains. If life has 

 developed on earth in the manner here indicated, why does 

 living substance no longer continue to form ? The conditions 

 under which life is being actually maintained on earth suggest 

 the direction in which many look to find an answer to this 

 question. Herbivorous animals obtain their food exclusively 

 from plants ; carnivora live on the flesh of the herbivora ; 

 thus they, too, in the final analysis, are nourished exclusively 

 by plants. Fungi, too, are dependent upon plants, to which 

 they are parasites, either directly or through the medium of 

 animals. Green plants are thus the great purveyors of nutrition 

 to all other living organisms. They themselves obtain their 

 mineral and nitrogenous food from the earth, and the 

 indispensable carbo-hydrates from the atmosphere, but they 

 can do this only by means of the sun's rays. Hence it is the 

 sun, and the sun alone, that ultimately supports life on earth. 

 If this is true, and it is indeed incontestable, we are naturally 

 led to ask whether it was not the sun likewise that originated 



