26 THB STBUaGLE FOE EIISTEHCE. 



size are in general perfectly safe against most of them. 



(b) Attacks of parasitic and epiphytic plants. — 'Tliese plants are 

 no respecters of age; but it is evident that the older a tree is, the 

 more Ukely is it to survive the attacks of all such plants other than 

 fungi. 



(c) Injurious climatic influences — -frost, drought, sunstroke, hail, 

 rain, wind, snow, lightning, 8fc. — The extent of difference between 

 neighbouring plants as regards size and vigour being, in the present 

 Case, practically unhmited, the remarks made in the First Case un- 

 der this head apply here vnth greater force. Young plants coming 

 up under lofty trees, wiU be perfectly safe against frost, hot and 

 cold winds, and snow, and, to a great extent, also against drought 

 and hail; on the other hand, the drip from the trees above might 

 prove hurtful or even fatal to very young seedlings. Again, the 

 older individuals, with their large and long roots, extending every 

 where in the direction of moisture, wiU in general be secure against 

 the severest and most protracted drought. 



(d) Conflagrations, — The remarks made under this head in the 

 First Case apply here in their fullest force. Even in the severest fire 

 very few large trees are killed outright, and the majority of them suf- 

 fer only a relatively sHght retardation of growth due to the scorch- 

 ing of the foliage, the death of some of the bnds and of the more her- 

 baceous twigs and shoots, and perhaps the charring of some portion 

 of the bark as far as the cambium. Indeed, iuPinus longifolia forest 

 ■the flames seldom attain the height of the crowns, so that it is not 

 uncommon in tracts of that species to see, after a fire has passed 

 through, the poles and larger individuals merely blackened for a few 

 feet up their boles, but otherwise apparently uninjured. On the 

 other hand, the smaller individuals suffer severely, and the extent of 

 the injury increases in geometrical progression as their size dimi- 

 nishes, being greatest in the case of species that cannot coppice. 



What has been said in the preceding paragraph refers exclusively 

 to the vitaHty and growth of the plants, not to their soundne';^ Forest 

 fires never fail to produce unsoundness ; but unsoundness by no means 

 necessarily imphes want of vitaUty, for a tree may be in the fuU vi- 

 gour of growth and yet be completely hollow or otherwise unsound. 



(e) £looJ'.-'n,evB is not much to add to what has been said 

 under this head m the preceding Case. The extent to which floods 

 may injure the various plants of a crop will b,e directly proportional 

 to the difference between their respective sizes, the advantage being 



