58 THE STEUGGLE POE EXISTENCE. 



the abundance and frequency with which they flower and seed (see 

 Condition XII, a and h). 



(c) Light, its .intensity and duration.. — Here also it is the action 

 of extremes that exercises any appreciable influence on the strugs;le 

 for existence, excessively bright Hght having the effect of over- 

 transpiration and insuiScient brightness the result of enfeebled as- 

 similation, the extreme limits being different for different species 

 and the difference being generally very much more marked in the 

 case of the lower limit, Some species cannot make any vigorous 

 growth except under exposure to direct sunhght. These form the 

 majority of our Indian species, and include teak, sal, &c.; but 

 amongst them there are many which are able to persist, and even 

 push on gradually, withHttle illumination. Thus Hardicickia linor- 

 ta, Anogeissus, &c., can resist long-continued suppression, and sal, 

 most of our climbers, and others can, unless the cover be very thick, 

 also slowly strengthen themselves and work their way up. Other 

 species, however, like the Quercus incana, silver fir, many laurels, 

 &c., vrill flourish and attain their finest dimensions even in more or 

 less diffused light. The figs require a great deal of direct sunshine, 

 and hence their arboreal habit. Going out of India to Northern 

 Europe we have the Scots' pine and birch delighting in almost per- 

 petual sunshine during half the year, and able to survive almost end- 

 less night during the other half. As rather mor« than one-half of 

 India is situated within the Tropics, and of the rest the greater por- 

 tion consists of level ground fully exposed to the sun and within a 

 few degrees of the Xorthern Tropic, the cHmatie influence of light 

 on the struggle for existence, except so much of it as was consider- 

 ed tmder Condition IV, is of comparatively secondary importance 

 save for those few species, such as the Finns excelsa, deodar, and 

 some other Himalayan trees, which require bright illumination, but 

 cannot sta,nd heat, both of which conditions are reahsed at the al- 

 titudes at which they grow. But this is anticipating subhead (e) 

 below. The discussion under Condition IV should be carefully 

 read in connection with the preceding observations. 



Besides affecting the relative development of tlie individuals of a 

 forest crop, according to the species to which they belong, the great- 

 er or less intensity of the hght acting on their crowns also exercis- 

 es a powerful influence on the frequency and abundance with which 

 they flower and seed (see Condition XII, a and h). 



(d) Aspect. — Change of aspect may introduce changes in all or 

 any one or more of the following conditions affecting the o-rowth of 

 plants: — diurnal and seasonal oscillations of temperature, quantity 



