CONSERVATORS’ WORK 147 
the victory of the mangroves, which themselves 
disappear so soon as out of reach of the tides. We 
may indeed suspect that an endless succession of 
crops of hard-wood is not entirely possible, for there 
is reason to fear that the toxic effect of the excreta 
of gregarious trees may be inimical to the con- 
tinuance of seedlings of the same species ; and it is 
certain that the mixture of species such as is found 
in a natural forest is provocative of healthy vitality, 
and that, in pure plantations, insects and fungi find 
a pleasant field for their enterprise. Such know- 
ledge leads us to pause in the endeavour to unduly 
increase the proportion of the more valuable timber 
trees, though we are checked more by the practical 
results of our experiments than by having entirely 
fathomed the causes that compel these results. 
Moreover, we suspect that such chemical constit- 
uents of the soil as are necessary to tree-growth 
are present in almost every soil in sufficient quantity 
to support tree-life, and that the physical qualities 
of the soil are those that have an even greater 
influence in the maintenance of a forest. There 
remains, then, to be discovered what other, if any, 
additions to a soil are responsible for hindering the 
indefinite continuance of any one species, and 
whether there may not be an interposition on the 
part of Nature prohibitory. of interbreeding, whose 
ill effects are so marked in the animal kingdom. 
We may some day light upon the causes that are 
at work when studying, as we now do, to remedy 
their effects, and then will become open to us those 
silvicultural secrets with regard to teak, to “ sal,” 
to other valuable Indian timbers which at present 
