These are in a general way similar to the potato with respect to the relation between dietary properties and biological function. The roots we employ as foods are those which are highly modified as storage organs, and resemble the potato in possessing a very high water and starch content and but very little protein. In the case of the sugar beet, the sugar replaces starch in a great measure. As in the potato there is a cellular layer at the periphery, but the interior is loaded with reserve food-stuffs. Appropriate feeding tests have shown that the properties of the beet resemble those of the seed and tuber rather than those of the leaf (28). The fleshy roots, the dasheen and sweet potato, have an inorganic content which resembles that of the seeds in a general way, so that an inspection of the analytical data relating to the composition of the ash of seeds, tubers and roots gave no promise that combinations in diets of seeds with either of the latter classes of food-stuffs would correct the inorganic deficiencies of the former. Feeding tests in which the seeds and tubers or roots have been combined and so supplemented with purified protein, and butter fat (fat-soluble A) that all the deficiencies of the mixture except the inorganic were made good, have given interesting results. The mineral elements derived from the natural foods in the mixtures, are not furnished in proportions to meet the nutritive needs of a growing animal. It is the low content of calcium, phosphorus, sodium and chlorin which is responsible for the failure of the animals, for when these are added along with protein and fat-soluble A, growth proceeds in the normal trend.

In the dry state, therefore, the fleshy roots resemble the seeds in food value. There is, however, one difference which should be mentioned. Like the potato and unlike the seeds the fleshy roots contain a large part of their nitrogen in forms which are chemically much simpler than protein. A part of this nitrogen is actually in the forms of digestion products of protein, and these are of the same value as protein. This value depends entirely on the presence of a complete list of amino-acids necessary for the construction of body proteins, and on the proportions in which they occur. There is always a part of the nitrogen in the form of other complexes which have no nutritive value.

A study of the carrot has been made by the biological method by Denton and Kohman (29). Their results show that it was possible to maintain young rats for some weeks on a diet composed exclusively of carrots, supplemented with sodium chlorid and a calcium salt, but the animals were not able to grow. They found it necessary to supplement the protein, and augment the fat-soluble A content before the rat was able to maintain growth even in an approximately normal manner.