2 EXPLOITATION OF PLANTS 
Nature, and it is evident that this number will go on 
increasing indefinitely. Nevertheless, until the secret 
of the universal function of green plants, the chloro- 
phyll‘mechanism, has been discovered, we shall be well 
advised to hold fast by the plant as the giver of nearly 
all good things. Even if we suppose that one day 
cellulose will be made synthetically, it is hard to believe 
that it will ever be possible to manufacture it in a form 
to compete with timber and vegetable fibres as they 
are given us by plants. 
Actually the triumphs of synthetic chemistry often 
serve to stimulate a threatened plant industry to re- 
doubled efforts. Thus synthetic indigo has not yet 
driven the natural product from the field. The effect 
of competition is to eliminate waste on the one hand, 
and on the other to call forth a more economic pro- 
duction, an increase of the output of indigo per plant, 
partly by cultural means, partly by improving the 
strain. As a consequence of the relaxation of competi- 
tion with synthetic indigo, due to the war, it is interest- 
ing to see that the natural product has received a new 
lease of life. For we read that the acreage of the 
current crop in India has been doubled, and that the 
output is expected to be increased in 1917 by some- 
thing like 75 per cent. as compared with 1916, 
The products which we derive from the vegetable 
kingdom are without number, and it is possible in a 
little book like this to attempt to deal with only a very 
small selection indeed. 
These products vary in the complexity of the manu- 
facturing processes required to make them available, 
