Agricultural Cliemidry— Turnips, 6b7 



buted to the bulb, notwithstanding its large amount of water, in 

 some respects a higher condition of elaboration, or fixedness in 

 its solid constituents^ than to the leaf. We have, indeed, supposed 

 that bulb formation, in the degree in which it is developed for 

 feeding purposes, is a deposition of matter existing in quantity 

 beyond what is essential to the health of the natural plant, much 

 as depositions are known to take place in animals under some- 

 what analogous circumstances. 



The following comparative statement of the proportion of ash 

 in the dry matter of the leaf^ the bulb, and the seed of the Norfolk 

 white turnip, will favour the view that the composition of the bulb 

 implies a more advanced selective process than that of leaf: — 





Leaf. 



Bulb. 



Seed. 



Percentage of ash in the dry matter of . • • . . 



9-5 



6-9 



4-5 



There is then, comparing one organ with another, as well as 

 different specimens of the same organ, a diminution in the pro- 

 portion of the mineral to the organic constituents of the plant the 

 further we advance towards the matured results of the vital process. 

 It is true that even in the seed the amount of mineral substances 

 is greater than our conceptions regarding the composition of the 

 definite compounds of which it is made up would alone have led 

 us to anticipate ; but numerous experiments with wheat grain 

 show that, however small may be the differences exhibited in a 

 series of specimens which can be compared with each other in this 

 respect, yet they will indicate the less percentage of ash in the 

 dry matter the higher the percentage of the dry matter itself — 

 that is to say, the more completely ripening processes have been 

 developed. An excess of mineral matter in any such case may to 

 some extent therefore be owing to an increased proportion of 

 vascular contents to perfectly elaborated substance. 



Admitting that the mineral substances found in the leaves of 

 the turnip and of other plants are such in variety and in amount 

 that we cannot suppose them to be all destined to enter into com- 

 bination, and actually to constitute a portion of the fixed and 

 essential formations of the plants, yet their presence within it is 

 not on that account quite inexplicable. The experiments of De 

 Saussure and others show that the rootlets of a plant take up the 

 dissolved substances presented to them, exercising but little of 

 selective power, whilst such as they have is rather of a mechanical 

 than of a more purely vital kind. It is not to be wondered at, 

 then, that the composition of the ash of highly vascular vegetable 

 substances should exhibit a wide range of difference, according to 

 climate, manuring, and soil. In such cases a large proportion of 



