THE WORLD’S CEREAL AND FOOD-CROPS 43 
become more largely agricultural, the need. for -new 
sources of potassium or even for phosphorus cmajy 
diminish, since they are not lost but are largely returned. 
to the soil. Co 3 
The facts we have just reviewed indicate} however, 
that there are after all very real limits to the possibilities 
of agriculture and to the population that is-dependent 
upon it. The somewhat popular notion that ‘h"ine 
tensive system of agriculture can be almost illimitably 
developed, so as to meet all possible difficulties that 
can arise in respect of food-supplies, is invalid: it is 
without basis. Indeed to obtain fertilisers economic- 
ally in sufficient quantity to meet the needs of even a 
small multiple of the existing 1950 millions of popula- 
tion will be very difficult, and will involve the use of 
more expensive methods than those characteristic of 
the present time. 
There is, too, a prevailing popular notion that, in 
some way or other, the developments of science will be 
such as to meet any difficulty of this kind. It has even 
been thought that the question of food-supplies can be 
met in perpetuity, and under all circumstances. This 
notion has, however, no valid foundation whatsoever. 
It is one of those surmises for which there is no warrant 
from any reasonable point of view. It is of course 
true that, with every accession of scientific and technical 
knowledge, a possibility of the earth carrying a larger 
population collaterally arises. The science and inven- 
tion of the last one hundred years, as already said, have 
actually enormously increased human population by 
increasing the food-supply, by making life-conditions 
better, and by reducing human mortality. But it is 
inevitable that the rate of such advances will slow down 
and ultimately that they will cease, in fact in a much 
shorter time than is popularly believed. Even as far 
back as the time of Quetelet (1796-1874), a contem- 
porary, Verhulst, submitted a theory that a territory 
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