84 BX VIRIBUS VIVIMUS. 



Mere size acts in plants and animals both, in 

 rendering them less susceptible to the cold of the 

 wet season, or the winter, and thus protracts life. 



The production of woody fibre in plants is a con- 

 dition of longevity, arid anything directly favouring 

 this may extend life. It enables the plant to resist 

 breakage by wind or other violence, and protects it 

 from cold. Thus bulbs continue the individual life 

 of an annual flower for many years, and thus the 

 trunks and branches of trees and shrubs live, whilst 

 the leaves and flowers die.^ Obviously the influence 

 on age of the development of wood is but a part 

 of the law of relation of evolution and longevity ; but 

 it is a special correlation, of very wide application. 



1 2. Some Experimental Evidence. 



There are some experimental proofs of the influence 

 of generative and personal expenditure on longevity 

 which may be now cited. By preventing plants from 

 reproducing, that is, by cutting off their flower-buds, 

 the gardener increases the bulk and the longevity 

 of some plants ; leaves and wood being produced in 

 place of generative products. By change from a 

 warm to a colder climate, this may similarly be 



' Some persons -hrould wish to regard tree-stems, bulbs, &c. as a 

 kind of asexual reproductive mass, and would look upon the flowers 

 of each year as successive generations of individuals. The compound 

 nature of perennial plants is one of the difficulties met with in attempting 

 to define individuality. 



