greater number of hours, or move to more distant fisheries, if they wished to obtain as much as they did at first. It is evident, however, that this diminishing productiveness of food-producing industries (and of all "extractive" industries, under which term are included agriculture, mining, and fishing) is made much more rapid than it otherwise would be by an increasing population. Another thing was observed by those whose business it was to bring to the island a sufficient supply of plantains. Doubling the amount of labour engaged in gathering the plantains did not even at first double the quantity of fruit they were able to bring home. At first, five men were able in two hours to gather as many plantains as would fill their boat. But they could not in four hours gather enough to fill two boats. Because, in the first two hours, they would gather the largest, and those that were most easily reached. In the second two hours, they had to gather smaller specimens, and those that grew in places where they were not so quickly reached. If you took four boys to a cherry-tree, and told them they
