24 THE PLANT. 



same amount of nourishment as from the larger, the 

 former must contain more of it, in proportion as the 

 absorbent root-surface is smaller. 



The ash of all plants in whose organism large quantities 

 of amylum, gum, and sugar are produced, is distinguished 

 from the ash of other plants by the preponderance 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 forma- 

 tion 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 dependence 

 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 of azotised 

 or non-nitrogenous substances are found combined in its 

 organism. 



To enable a plant to attain its maximum of growth, 

 the soil must at all times yield, in an available form, the 

 whole quantity of each of its constituents ; and, on the 

 other hand, the cosmic conditions — heat, moisture, and 

 sunhght — must cooperate to transmute the absorbed 

 substances into the organs of the plant. If the substances 

 that have passed from the soil into the plant cannot be 



