4 EXPLOITATION OF PLANTS 
becomes profitable for the planter to step in and give 
us, e.g. plantation rubber. 
In the case of crops raised under control, it is of the 
greatest importance for the cultivator to realise at the 
outset for what precise purpose his output is destined. 
With this knowledge he may at every stage in cultivation 
—by selection of variety, by manuring, thinning, 
pruning, and so on, promote a close approximation to 
the specification. The forester should consider the 
requirements of the carpenter; the tea planter the 
taste of those he desires to pay for the privilege of 
sipping his beverage; and equally in other cases. 
Exploitation without consumption.—This is a branch 
of the subject which, not being dealt with elsewhere in 
this book, may receive passing reference here. It is, 
briefly, the department of economic botany wherein 
plants are employed as a substitute for the constructions 
of the engineer, more especially the rendering of ground 
which is mobile, from whatever cause, secure. Hitherto 
it has been practised only in occasional instances, 
and its possibilities are not realised as fully as they 
should be. 
The best-known example and the most highly 
elaborated is the planting of sand dunes with marram 
grass (Psamma) and other sand-binding plants. The 
technique of dune protection by planting, though 
developed into a fine art in Gascony and the Baltic, 
is not well enough known in quarters where it might 
be of service. 
Other cases to which planting is applicable are those 
of travelling beaches, eroding cliffs, the banks of rivers, 
and steep sloping ground liable to crumble or develop 
