MIXED CHOP OF UNIFORM AGE. 41 



(xvi) Slope of ground. A tree on a steep bank or slope will 

 naturally suffer more than others on less inclined ground, not only 

 from the flames mounting higher as the fire rushes uphill, but also 

 by reason of the mass of dry twigs and other inflammable matter 

 caught by the trunk on the upper side. 



(xvii) Size and consistence ot leaves and quantity shed. The 

 needle-shaped leaves of conifers naturally settle and form a closer 

 mass than the large, flat leaves of broad-leaved species, which 

 therefore flare up higher and quicker, and give out a more intense, 

 if not os prolonged and steady a heat. Moreover, these leaves, 

 owing to the broad surface they offer with a minimum of weight, 

 are easily carried high up in a burning state, often to more than a 

 hundred feet, by the uprush of hot air, and thus increase the risk of 

 the green crowns catching fire. Conifers have, in almost every case, 

 also another advantage, and that is that, as their leaves persist for 

 two years and upwards, they shed at any one time only a portion of 

 their foliage. The thicker and more woody leaves are, the greater 

 and more prolonged will be the heat they will give out in burning. 



(xviii) Imflammability of the bark and dead leaves and wood due 

 to presence of oil or resin. In this respect conifers stand at a very 

 great disadvantage. It is a notorious fact that in a forest fire 

 more green standing individuals of some species are burnt down 

 than of others. 



(xix) The quantity of moss and ferns growing on the trunk 

 and branches. If the quantity of such epiphytic vegetation is so 

 large as to form a complete loose envelope round the trunk and 

 branches, it must, when dry, enable fire to mount up into the 

 crowns, killing the cambium and all buds and leaves, in the other 

 words, the entire tree, Such a catastrophe is very common when 

 conflagrations occur in the moist temperate forests of the eastern 

 Himalayas. 



(xx) The time when any fire in question occurs. On this 

 will depend the quantity and dryness of the combustible matter 

 present and consequently also the absolute severity of the fire. 



(xxi) Exacting nature of the various species as regards rich- 

 ness of the soil. Fires consume all the fallen leaves and other 

 vegetable detritus. It is true that in the ashes they leave behind 

 they render at once available the entire mineral constituents of 

 plant-food present in that detritus ; but that is no compensation at 

 all for their inevitable dissipation of the organic elements, the con- 

 tinued presence and transformation of which into new compounds 

 would, besides ultimately returning to the soil all the mineral and 



