92 THE STRUGGLE FOR EXISTENCE. 



The most important point under this condition is the power of 

 growing up again from the stool. All species possessing it lose it 

 after a certain age varying with the species in question. It is, 

 <luring the first years, only slight, then increases rapidly with the 

 diameter of the tree up to the middle of the high-pole stage. Thence- 

 forward it remains unchanged for a series of years varying with the 

 species concerned, after which it gradually or suddenly diminishes. 

 Hence, where clearings or fellings on an extensive scale have been 

 made, the new crop may consist principally of species that are not 

 necessarily the strongest for the battle of life, for such species may 

 have been represented in the original crop chiefly by old trees past 

 their coppicing age, while the majority of the individuals of the 

 other were young enough to coppice. 



XV. RELATIVE FACILITY OF THROWING UP ROOT-SUCKEKS. 

 The faculty of throwing up root-suckers is at first nil, then increases 

 with the spread of the roots until the tree begins to decline, when 

 the roots gradually become feebler and die off at their extremities, 

 so that the entire root-system contracts and the number of the 

 smaller roots and root-fibres, on which the sucker-producing adven- 

 titious buds principally originate, suffers very considerable diminu- 

 tion. 



XVI. RELATIVE DURATION OF FOLIAGE AND SEASON OF ITS 

 FALL AND RENEWAL. It is an almost invariable rule that in the 

 case of every species the younger individuals not only retain their 

 foliage longer, but also bring out the seasonal or annual flush ear- 

 lier ; and that, if by any chance the foliage of the season is de- 

 stroyed, the young individuals (not always, however, the very 

 youngest, since they are poor in dormant buds) renew it earliest, 



XVII. A CLIMBING HABIT. It is only after the first few years,, 

 when the young plant is thoroughly established, that a climber begins 

 to nutate or throw up shoots which develop tendrils or adventitious 

 roots or which are long enough to scramble up other trees or 

 shrubs. Once this pei'iod is reached, age has 110 further effect as 

 far as the climbing habit is concerned. 



XVIII. AN ARBOREAL HABIT. This is a new Condition, since 

 an arboreal habit necessarily implies the existence of different ages. 

 Plants possessed of this habit are either (i) parasitic, like Cuscuta, 

 fungi, &c. ; or (ii) only partially parasitic, like Visc-nm,, Loranthus, 

 &c. ; or (iii) purely epiphytic, like some figs, Araliaceip, &c. 



Parasites and epiphytes generally have already been taken ac- 

 count of under Condition III (7/) as injurious "causes extraneous- 

 to the forest." In this place we have to deal with only such of 



