28 THE STRUGGLE FOE EXISTENCE. 



ih foliage on the same level as the crown of that tree, and thus leave 

 ?ome of the overtopped stems unmolested, while keeping back their 

 overtopping rival. In this way may be explained the freedom 

 IV. m climbers of many young individuals in dense forests, although 

 the climbers may be almost as numerous as the trees themselves. 



IV. COMPLETENESS OF THE LEAF-CANOPY. Light is not neces- 

 sary for germination, for the young seedling develops, and can even 

 make a certain amount of growth, by means of the reserve matter 

 stored up in the seed. But once that reserve matter has been uti- 

 lised by the seedling, this latter must die if it is unable to assimilate 

 food for itself ; in other words, it cannot do without light. While 

 the seedling is still small and makes but little progress, and, on that 

 account, wants but little food, illumination more or less feeble 

 suffices; but, as with increasing size and increasing rapidity of 

 growth its wants increase, the requisite amount and intensity of 

 illumination necessarily increases in proportion. As regards cop- 

 pice shoots they must, because of their very much more rapid early 

 growth and much larger size at first, obviously receive a considerable 

 amount of light almost from the very moment that they make their 

 appearance. The requisite degree of illumination will depend on the 

 size of the parent stools, roots or rhizomes. Thus, whereas small 

 seedling-shoots scarcely require more light than true seedlings of 

 their own size, the strong shoots that come up on well-nourished stools 

 of middle age will be almost as exacting as saplings and poles nearly 

 three times as large again as themselves. But while both seedlings 

 and coppice shoots require an ever increasing amount of light as 

 they push up, they can survive for a certain time on very much less 

 than this, the length of time varying with the degree of endurance of 

 shade of the species in question and with the age of the plants. Thus 

 deodar and silver fir, both remarkably shade-enduring species, may 

 survive under a very dense leaf-canopy until they are 40 years and 

 upwards old, whereas seedlings of Pinus longifolia and teak, which 

 are very partial to light, cannot persist under fairly dense cover for 

 more than 10 to 15 years, and teak stool-shoots for barely 5 years. 

 But because young plants can survive under cover up to a certain 

 age, it does not follow that they will also retain as long the full power 

 of recovery on being admitted to the influence of light. After a cer- 

 tain time the cambium becomes weakened owing both to insufficient 

 transpiration and assimilation, and to the increasing pressure to 

 which it is subjected between the growing woody layers on the inside 

 and the hard, dry bark on the outside, and the result is that the plants 

 become, to use a popular term, hidebound. If they are broad-leaved, 



