The important part which the so-called root crops play in the modern systems of agriculture, has secured for them a large share of the attention of the chemist, so that our knowledge of their composition and relative nutritive value is very extensive. As compared with most other articles of food, the roots, as they are popularly called, of potatoes, turnips, mangels, carrots, and such like plants, contain a high proportion of water, and are not very nutritious; indeed, with the exception of the potato, none of them contain 20 per cent. of solid matter, and some not more than five per cent. They are, however, easily produced in great quantities, which compensates for their low nutritive value. I shall consider each of the more important roots separately. _The Turnip._--There are numerous varieties of this plant, which differ from each other in the relative proportions and total amount of their constituents, and even in different individuals of the same variety there is considerable variation in composition; hence the difficulty which has been felt by those who have endeavored to assign to this plant its relative nutritive value. From the average results of a great number of experiments, conducted both in the laboratory and the feeding-house, it is concluded that turnips are the most inferior roots produced in the field. The Swedish turnips are the most valuable kind: they contain a higher proportion of solid matter than the other varieties, and they are firmer and store better. The average composition of five varieties of turnips, as deduced from the results of the analyses of Anderson and Voelcker, is shown in the following table:-- ANALYSES OF TURNIPS. ----------------------------+-------+-------+--------+---------+------- |Swedish| White |Aberdeen|Purpletop|Norfolk |Turnip.| Globe.|Yellows.|Yellows. |Bell. +-------+-------+--------+---------+------- Water | 89·460| 90·430| 90·578| 91·200 | 92·280 Albuminous, or | | | | | flesh-forming substances | 1·443| 1·143| 1·802| 1·117 | 1·737 Non-nitrogenous, or | | | | | fat-forming substances | | | | | (fat, gum, sugar, &c.) | 5·932| 5·457| 4·622| 4·436 | 2·962 Woody fibre | 2·542| 2·342| 2·349| 2·607 | 2·000 Mineral matter (ash) | 0·623| 0·628| 0·649| 0·640 | 1·021 +-------+-------+--------+---------+------- |100·000|100·000| 100·000| 100·000 |100·000 ----------------------------+-------+-------+--------+---------+-------