354 THE LIFE OF THE PLANT 



moreover work the whole year round. How far he will 

 succeed is for the future to decide. One thing is certain, that 

 when by means of his artificial apparatus man shall gather from 

 all the free area of land about a hundred times more organic 

 matter than is contained in the richest crop to-day, he will 

 be able to say that he has reached the limit ; that he can 

 go no further. Man will then make no further demand of the 

 soil or his art, for more fuel or more food he will not be able 

 to get any more, because the sun will not be able to give 

 any more. Then the law of Malthus will manifest itself in 

 all its ominous cogency: mankind will have to keep a strict 

 account of life and death ; it will have to take account of the 

 death-rate before reproducing itself, as has been already anxiously 

 suggested by perspicacious economists. No extra mouth, in the 

 literal sense of the word, will then find room at the banquet 

 of Nature. Will mankind ever attain this limit ? By what new 

 processes of synthesis will Berthelots of the future benefit it ? 

 What new sun-machines will be furnished by future Mouchots 

 and Ericssons ? Who can tell ? One thing is certain, that our 

 planet will acquire then a very dismal aspect. When man shall 

 have arrived at the utilisation of all the energy of the sun 

 instead of only part of it as we do at present, then, instead of 

 the emerald green of our meadows and woods, our planet will 

 be covered with the uniform mournful black surface of artificial 

 light-absorbers. Lord Kelvin foretold that our planet will find 

 its death from cold, that our world would be wrapped in its 

 icy embrace; but I do not think this prophecy has alarmed 

 more than a very few. It will come to pass long after our day, 

 and we all know the proverb: apres moi le deluge. Yet we 

 cannot help shuddering at the idea of what life will be like 

 when the earth is transformed into a universal factory, with no 

 possible escape into the open even on a holiday, even for a single 

 hour ! 



Let us turn from this gloomy and fantastic picture of what 

 I am happy to say is a very remote future, and go back to 

 the question raised at the beginning of this lecture, which 

 we are now able to answer fully and categorically. We can do 

 so best under the following figure. Once upon a time a ray 

 of sunlight fell somewhere upon the earth. It did not fall, 

 however, upon sterile soil, but upon a green blade of wheat, 



