MIXED CROP OF VARIOUS AGES. 93 



tlieni as form an integral portion of the forest and have to struggle 

 against other plants for a place in it. Under this category come 

 only some of the species falling under class (iii). 



In the case of trees, which like the figs, are epiphytic only at 

 first, but ultimately become terrestrial as soon as their roots reach 

 the ground, the epiphyte is bound to prevail over its temporary 

 host, firstly, because it appears at once in the light on the sum- 

 mit of its host where it can never be suppressed, and next, be- 

 cause, as a rule, the mass of its long stem-like amalgamating roots 

 ultimately encloses and grows round the trunk of the host, which it 

 completely strangles. 



The epiphytic Araliacea*, nearly always also of climbing habit, 

 do not, as far as we know, kill directly their hosts, but only weaken 

 and deform them, in very much the same way, but to a much less 

 extent, as non-twining climbers do. 



General Remarks. 



From what precedes it will have been gathered that a mixture 

 of different ages is particularly favourable to the maintenance of a 

 mixture of species. We have already seen that uniformity of age 

 throughout a mixed crop tends to reduce the number of species 

 and, in most cases, to give an easy preponderance to a single one, 

 the most tenacious and exclusive of the original mixture (Third 

 Case, p. 83). So that the converse is also true, viz. that a variety 

 of ages always promotes a mixture of species and is often an in- 

 dispensable condition for growing a mixed crop: it gives a certain 

 chance of existence to species which would otherwise be driven 

 out by their more tenacious and exclusive companions. A cursory 

 examination of a sal forest, to take a common instance that strikes 

 the eye at once, is sufficient to convince oneself of the truth of this 

 proposition. Where the trees are all of a more or less uniform 

 height, and, therefore, presumably of about the same age, they are 

 almost exclusively sal ; whereas, where ages vary, many other 

 species will be found associated with the sal, the relative propor- 

 tion of those species generally increasing with the difference or 

 ages. There can be no doubt that the pure character of the ex- 

 tensive teak copses of the Central Provinces, Berar, and Bombay 

 are, in a great measure, due to a certain marked degree of unifor- 

 mity of ages; it will generally be found that the purest of these 

 copses are those in which the trees are pretty nearly of one and the 

 same height. 



