P0EB CHOP OF MIXED AOES. 25 



I. Relative innate vigour. — The importance of this condition 

 here is not so great as in the First Case, since a difference of ages 

 may quite nulHfy it. Nevertheless greater age is not necessarily a 

 criterion either of greater vigour or of greater debihty, for the cop- 

 pice yearKng shoot wiU, as a rule, be always very much more vigorous 

 than a seedUng several years old, and an aged tree may not unfre- 

 quently be more tenacious of existence than another in the prime of 

 life. 



II. Greater suitability of soil and subsoil. — In the re- 

 marks made under this head in the preceding Case, it was explain- 

 ed that in unfavourable soils resting on a bad subsoil disparity of 

 size may give the victory to the less advanced individuals. That 

 remark may be repeated here with greater emphasis, since, in the 

 present Case, the disparity between a plant and its neighbours 

 may have no practical limit. When the subsoil is impenetrable 

 sheet-rock or clay, or is impermeable to water, or, on the other 

 hand, is so permeable as to be entirely waterless for the purpose of 

 vegetation, the younger plants may be able to live on, while the 

 older wither, decay, or die off as soon as their roots reach this 

 unfavourable subsoil, having it may be, in the meantime, while 

 struggling to establish themselves, improved and prepared it for the 

 younger growth. So also when the soil and subsoil are very poor, 

 the older and larger plants, requiring a larger sum of nourishment 

 than the soil can supply, may become stag-headed and thus open out 

 the leaf-canopy for the younger individuals. Where, the subsoil not 

 being utterly bad, the soil above is very stiff or very wet, the older 

 plants will generally possess the advantage, since with their more 

 woody and stronger roots they will the better resist breaking and 

 ejection during the successive contraction and expansion of the soil 

 tinder the influence of alternations of drought, moisture and frost, 

 and with their larger root and leaf- systems, guaranteeing a suffici- 

 ently rapid absorption and transpiration, also escape wet feet. 



III. Death, disease, unhealthy state or retardation of 



GROWTH DUE TO CAUSES EXTRANEOUS TO THE FOREST, viz. — 



(a) Attacks of insects avd other animals, — Insects attack young 

 and old ahke, but unless these pests are very numerous or very 

 voracious, the older plants, provided they are not yet in their dechne, 

 will obviously possess greater powers of resistance than those that 

 are younger, especially if the insects in question are phyllophagous. 

 As against other animals hurtful to vegetation, greater age gives 

 a very marked advantage, so much so that plants above a certain 



