THE CRITERIA OF LIVINGNESS 91 



the duration of individual life at the one extreme. The 

 Big Trees living for two thousand years may be near the 

 limit in the other direction. 



4. The Capacity of Growth, Reproduction, and 

 Development. 



One can readily conceive of an organism which balanced 

 its accounts from hour to hour, but never had much margin. 

 There are such delicately-poised ephemeral organisms, which 

 live, to use a homely expression, from hand to mouth. They 

 are going concerns, but they are trading on a very restricted 

 capital, and cannot survive a crisis. So we see at once that 

 there is a commanding advantage in being able to store energy 

 in potential form, and this is fundamentally characteristic 

 of organisms especially of plants. As regards the ratio 

 between the income of energy and the work done, living 

 organisms are far ahead of any engine, but there is also 

 the power of accumulating energy which can be used later. 

 Thus we are led to recognise the power of growth as one 

 of the characteristics of organisms. A surplus of income 

 over expenditure is the primal condition of organic growth. 

 It has further to be noted that the growth of living creatures, 

 as contrasted with that of crystals, is at the expense of 

 materials different from those which compose the organism; 

 it implies active assimilation, not passive accretion; and it 

 is very definitely a regulated process. An organism does not 

 grow like a snowball. 



But growth leads on to multiplication. As Haeckel clearly 

 indicated in his Generelle Morphologie (1866), repro- 

 duction is discontinuous growth. How impossible it is to 

 draw any hard and fast line between a fragmentation which 

 separates off overgrowths, and the more specialised modes 



