224 ARE THE INORGANIC CONSTITUENTS REALLY CONSTANT ? 



§ 5. O/* the alleged constancy of the inorganic constituents of plants, in 

 kind and quantity. 



In the preceding lecture (ix., p. 177), it was stated that the ash of the 

 same plant, if ripe and healthy, is nearly the same in kind and quality 

 in whatever circumstances (if favourable) of soil and climate it may 

 grow. This general observation, however, is consistent with certain 

 (lifferences in the above respect, whicfh are not without interest in their 

 bearing upon agriculture botJs in theory and practice. Thus, 



1°. The different parts of the same plant contain quantities of inor- 

 ganic matter, not only different in their gross weights, but unlike also in 

 the relative proportions of the several substances of which the entire ash 

 consists. Both of these points have been previously illustrated (pp. 179, 

 180), and they are placed in the clearest light by the tabulated analyses 

 introduced into the preceding section. 



2°. The quantity and relative proportions of the different inorganic 

 substances also vary with the season of the year at which the examina- 

 tion is made. Thus, according to De Saussure, plants of the same wheat 

 which a month before flowering left 7-9 per cent, of ash, left when in 

 flower only 5*4, and when ripe 3'v3 per cent. The quantity of potash 

 in the potato leaf diminishes very much as the plant approaches to ma- 

 turity (MoUerat) — and the same has been observed in many saltworts 

 and other sea-side plants. In the young plant of the salsola clavifolia 

 there is much potash and no soda, but as its age increases the latter alkali 

 appears, and gradually takes the place of the former.* 



It is probably true, therefore, of all plants — that the ash both in kind 

 and quantity is affected by the age at which the plant has arrived. It 

 would appear that the unlike chemical changes which take place in the 

 interior of the plant, at the successive periods of its growth, require the 

 presence of different chemical agents — or that the production of new 

 parts demands the co-operation of new substances. 



3°. Similar differences are sometimes observed also when the same 

 plant is grown in different soils. Thus it is known that the straw of the 

 oat grown upon boggy land is very different in colour and lustre, from 

 that yielded by the same variety of seed, when grown upon sound and 

 solid soil. I lately examined two such portions of straw from the same 

 seed — grown on the same farm on the estate of Dunglass, the one on 

 boggy, the other on sound stiff land, when the straw from the 

 Sound land left 6-64 per cent, of ash, and from the 

 Boggy land "■ 6-2 per cent, of ash ; 

 while the silica contained in the ash from the 



Sound land amounted to 3-42 per cent., and from the 



Boggy land " to 1*90 per cent, of the weight of the straw. 



A remarkable difference, therefore, existed in the relative proportions, 



• Meyen, Jahresberickt, 1839, p. 125. In regard to these salt-loving plants, which generally 

 aboSnd in soda, a curious observation was long ago made by Cadet. He states that if a plant 

 of common salt- wort (salaola aali) be transplanted into an inland district — and seed from this 

 plant be afterwards sown, the second race of plants will contain much potash, but scarcely a 

 trace of soda.— Gmelin's Handbuch der Chemie, JI. p. 1492. Potash may thus take the 

 place of soda for a time, but removed from its native habitat, the plant would in a few gene- 

 rations die out and disappear. 



