70 CHANGES OF COMPOSITION [chap. 



sugar in the root has been raised to eighteen or over. 

 The sugar-content of mangold has not been similarly 

 raised, because in its case the seed parents have been 

 selected only on a basis of size and shape and never on 

 the amount of sugar they contained, as determined by 

 analysis. The figures just given for the percentage of 

 sugar and dry matter in the mangold are of course only 

 averages; certain variations occur due to the soil, 

 manuring, and also season, but perhaps the largest 

 variation is that due to size. The larger the root the 

 more watery it becomes ; mangolds weighing approxi- 

 mately 2 lb. apiece contain about 2 per cent, more dry 

 matter than mangolds averaging 7 lb. apiece, above 

 which weight the falling off in dry matter is not so 

 marked. The age of the mangold has not much 

 influence, it possesses much the same composition all 

 the time it is growing ; just as the wheat grain is filled 

 up with material of approximately constant composition 

 from the beginning until the end of grain formation, so 

 as the mangold bulb swells it is being packed with 

 materials of a fixed type as regards the proportions of 

 dry matter, sugars, and nitrogenous matter, this material 

 being manufactured in the leaf Certain changes do 

 occur; in the immature mangold, as in those grown 

 with an excessive amount of manure, there is a slightly 

 smaller proportion of dry matter, while a much larger 

 proportion of the nitrogen contained in the root is 

 combined in the form of nitrates and non-protein 

 compounds. The nitrates and non-protein compounds 

 are far from having disappeared when the mangold is 

 ripe in the late autumn, though they are considerably 

 reduced in amount. If the mangold is allowed to grow 

 a second year for seed, a reverse series of changes take 

 place ; the sugar is removed from the cells of the root in 

 order to form the flowering stem and eventually the 



