36 THE STBVGQLE FOB EXISTENCE. 



have (1) the goat, (2) the sheep, (3) the camel, (4) the pig, (5) the 

 buffalo, (6) the cow and (7) horses, mules, and donkeys. 



(b) Attacks of parasitic and epiphytic plants. — All the remarks 

 made under this head for the First Case apply also here. Here we 

 need only add that parasites are nearly always selective, preferring 

 some species and genera to others, or living exclusively on a single 

 species, or on plants belonging to a single genus or family ; and so 

 also, although to a much less extent, with many epiphytes. Thus the 

 Arceuthobium Oxyeedri, as far as is known, grows in India only on 

 Juniperus excelsa and Pinus excelsa, gradually overspreading the 

 plant on which it has once taken root, and often killing the branch 

 or the entire tree. The fungus Peridermium Pini attacks at one 

 stage of its existence only various species of pines. Another fungus, 

 Trametes radiciperda, infests only conifers. And so on* 



(c) Damage caused by climatic influences. — Under this title we 

 will include only the injury suffered from the causes in question by 

 individual piavis irrespective of whatever general influence they may 

 exercise on the vegetation of each species considered collectively. 

 The consideration of that influence would introduce a much larger 

 question, whcih on account of its extreme importance will be treated 

 under a separate major head (see Condition X below). This reser- 

 vation being borne in mind, the remarks already made on the 

 subject of climatic influences under the first two Cases should be 

 read over again here. 



(d) Conflagrations. — In what way fires injure trees and forests 

 and on what general circumstances their degree of destructiveness 

 depends are questions which will be more appropriately treated 

 when we come to consider the subject of the preservation of forests 

 from fire. The student will, however, do well, before he proceeds 

 farther, to study Sections I and II of Chapter I, Book III. 



The various degrees of resistance offered to the effects of forest fires 

 by the different species composing the crop will depend on a great 

 many circumstances, the principal of which are the following: — 



(i) The evergreen or deciduous nature of their foUage. — The 

 more constant the leaf-canopy at any point is, the smaller will be 

 the quantity of combustible undergrowth, especially grass, on the 

 ground, the moister will be the soil, and the longer in consequence 

 will the undergrowth remain green and uninflammable. So that in 



* Precise information under this head ia wanting in India, and more careful and ex- 

 tended observations are urgently caUed for. At the present moment our knowledge 

 with refeience thereto is extremely meagre. 



