NITROGENOUS SUBSTANCES IN TUENIPS. 39 



substance is converted into a tasteless, gum-like body, 

 or into cellulose, or sugar becoming a constituent of 

 the leaves or of the roots, according as the organic 

 energy preponderates in the overground or under- 

 ground organs. 



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 must necessarily be much richer in phos- 

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

 period for 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 after- 

 wards ; hence, if the root is to draw from this smaller 

 bulk the same amount of nourishment as from the 

 larger, the former must contain more of it, in propor- 

 tion as the absorbent root-surface is smaller. 



The ash of all plants in whose organism large quan- 

 tities of amylum, gum, and sugar are produced, is dis- 

 tinguished from the ash of other plants by the prepon- 

 derance of potash ; now, if the potash in the sap of the 

 turnip plant formed a necessary agent in the formation 

 of sugar and the other non-nitrogenous constituents, the 

 quantity of that mineral matter absorbed in the third 

 and fourth stages of growth is easily explained because 

 the formation of the non-nitrogenous constituents of the 

 root was more active in these than in the former stages. 



That the production of the combustible constituents 

 the conversion of the carbonic acid and ammonia into 

 non-nitrogenous and azotised substances stands in a 

 definite relation of dependence to the incombustible 

 matter found in the ash, is an opinion which no longer 

 requires special proof to support it. But the depend- 

 ence is mutual. To say that the reason why the 

 azotised or non-nitrogenous products are formed in 

 large proportion is because the plant has taken up more 

 phosphoric acid or potash, is just as correct as to assert 

 that the plant takes up more phosphoric acid or potash 

 because the other conditions required for the production 



