The series representing the growth of the means of subsistence is also open to criticism. It is evidently of a more arbitrary character, and we cannot say whether it is simply supposed to represent a possible contingency like the first, or whether it pretends to represent reality. At least it does not correspond to any known and certain law, such as the law of reproduction. As a matter of fact it rather seems to give it the lie; for, in short, what is meant by means of subsistence unless we are to understand the animal and vegetable species that reproduce themselves according to the same laws as human beings, only at a much faster rate? The power of reproduction among plants, like corn or potatoes, or among animals, like fowls, herrings, cattle even, or sheep, far surpasses that of man. To this criticism Malthus might have replied as follows. This virtual power of reproduction possessed by these necessaries of life is in reality confined to very limited areas of the habitable globe. It is further restricted by the difficulty of obtaining the proper kind of nourishment, and by the struggle for existence. But if we admit exceptions in the one case why not also in the other? It certainly seems as if there were some inconsistency here. As a matter of fact we have two different theses. The one attempts to show how multiplication or reproduction need not of necessity be less rapid among plants or animals than it is among men. The other expresses what actually happens by showing that the obstacles to the indefinite multiplication of men are not less numerous than the difficulties in the way of an indefinite multiplication of vegetables or animals, or, in other words, that the former is a function of the latter.