NITROGENOUS SUBSTANCES IN TURNIPS. 23 



If wc regard the mere increase of the leaves and roots 

 in mineral substances, witliout reference to the total 

 amount of tlieni absorbed by the entire plant, it appears 

 to be most uTcgiilar, and to proceed by ' fits and starts.' 

 The plant receives every day nearly the same quantity of 

 phosphoric acid, nitrogen, salt, and sulphuric acid, which 

 are distributed in the several parts of the plant, leaves, 

 or roots, where they are required for use. The chief 

 difference observable is in the increase of potash, which 

 in the thkd stage is out of all proportion greater than 

 that of the other mineral constituents. 



It is highly probable that from the raw material — i. e. 

 the carbonic acid, water, ammonia, phosphoric acid, 

 sulphm-ic acid, with the cooperation of the alkahs, earths, 

 &c. — the chemical process engenders in the plant simply 

 a nitrogenous and sulphureous substance, belonging to the 

 albumen group, and only one non-nitrogenous substance, 

 belonging to the group of hydro-carbons. The former 

 retains its character during the period of vegetation ; 

 while the non-nitrogenous substance is converted into a 

 tasteless, gum-hke body, or into cellulose, or sugar — 

 becoming a constituent of the leaves or of the roots, 

 according as the organic energy preponderates in the 

 overoTound or underfi^round or^jans. 



C DO 



If there is a relation between the phosphoric acid and 

 the production of the nitrogenous constituents, the soil 

 must contain, in its parts, definite proportions of both 

 substances ; and for the cultivation of turnips, the upper 

 layers miist necessarily be much richer in phosphates 

 than the lower. For in the first half of the period of 

 vegetation, the branching of the roots is much less 

 extensive than at a later period, and the root is in contact 

 with a much smaller bulk of earth than afterwards ; 

 hence, if the root is to draw from this smaller bulk tlie 



