1S36.] 



FARMERS' REGISTER. 



139 



Potash is principally composed of a carbonate 

 of potassa, but contains, besides, silica, rendered 

 soluble by the alkali, sulphate and muriate 

 of potassa, and a peculiar acid known by the 

 name of ulmic, which is a compound of carbon, 

 hydrogen, an(i oxygen. The insoluble part is 

 made up of carbonate of lime, sulphate and some- 

 times phosjihate of lime, silica. The carbonate 

 of lime has probably in no case existed in the liv- 

 ing plant, but.arises from the destruction bj^ heat 

 of the peculiar acid of the plant; as, lor instance, 

 the citric, the oxalic, or the tartaric ; all of which 

 are by fire converted into carbonic acid. 



The quantity of ashes is extremely various, as 

 is their proportion of the several soluole and inso- 

 luble substances, we have mentioned. Thus the 

 ashes of the stalk of Indian corn yield 12^- per 

 cent, of ashes, while the soft woods do not furnish 

 more than two parts in a thousand. The propor- 

 tion of the sulphate and phosphate of lime is even 

 more various. Thus, in some cases the presence 

 of the sulphate is hardly perceptible, while of the 

 ashes of clover it forms a large proportion of the 

 whole weight. Phosphate of lime is found in the 

 proportion of fifteen per cent, in the grain of wheat. 



Water is not only one of the principal compo- 

 nent parts of all plants, but is also the sole vehicle 

 of their nutriment. At each extremity of the 

 small fibres into which the roots of plants are di- 

 vided, is an opening through which that fluid en- 

 ters ; and it appears that, except in the case of a 

 plant having lost its vigour by continued drought, 

 it is only through this channel that water can en- 

 ter. By a powerful action iidierent in living ve- 

 getables, water, which, with all the matters it is 

 capable of holding in solution, becomes the sap,* 

 is raised to the highest parts of the plants, and 

 forced to their most distant extremities. It has 

 been ascertained that plants do not possess the 

 power of rejecting even those substances which 

 are most noxious to them; it is therelbre probable, 

 that the character of the fluid admitted, is the 

 same in all the plants which grow upon the same 

 soil. Whether it undergoes any change in tlie 

 root does not appear certain; but it has recently 

 been maintained that every description of plant 

 throws off by the surface of its roots such mat- 

 ter as, it retained, would be injurious; but this 

 opinion does not appear to be well established. 



The sap, when carried up to the leaves, under- 

 goes an important chansre; principally owing to the 

 action of solar light. When exposed to light, the 

 leaves of plants give out oxygen in considerable 

 quantities. This proceeds Irom a decomposition 

 of the water und carbonic acid, the remaining ele- 

 ments of which two substances, and a portion of 

 their oxygen, enter into new combinations. These 

 combinations have different characters in different 

 vegetables, but are most flimiliarly known in the 

 shape of gum and resin. These still contain the 

 earthy and saline matter carried up by the sap, 

 and after they are formed, return downwards to- 

 wards the roots. In their descent they deposite the 

 several parts which minister to the growth of the 

 plant — the leaves, the bark, and the woody fibre. 

 They also appear to be forced with powerful ener- 

 gy into the flower and the growing fruit, and in 

 these a still more important action is carried for- 

 ward, by which the reproiluction of the species is 

 ensured. 



* SeeRopret's Bridjre water Treatise. 



The matters which the water that enters by the 

 root may hold in solution, are either derived "from 

 the atmosphere or from the soil. In its |)assage 

 through the air it will carry with it a considerable 

 proportion of carbonic acid, and all the sulphuretted, 

 hydrogen it meets with. It will also take up a 

 small quantity of oxygen, and of carburetted lay- 

 drogen, and a still less quantity of nitrogen. 

 From the soil it will take all the more soluble salts, 

 small quantities of sulphate, phosphate, and car- 

 bonate of lime, provided they be present, and sili- 

 ca. So also if the soil contain animal matter, or 

 vegetables of which nitrogen forms a part, the 

 ammonia generated by their decomposition will 

 likewise be dissolved by the water. In like man- 

 mer. the carbonic acid, which has arisen from the 

 decomposition of vegetable or animal matter, and 

 has not yet escaped, and the soluble compounds 

 of carbon, oxygen, and hydrogen, which are ge- 

 nerated by the same process, will have been taken 

 up, and carried by the water into the root of the 

 plant. It will thus appear that, contrary to the 

 opinion of Mr. Puvis, the atmosphere furnishes 

 but little of the fixed elements of plants, with the 

 exception of sulphur and carbon ; and that even if 

 the growth ol plants were to depend wholly upon 

 the carbon obtained in the form of carbonic acid 

 from the atmosphere, their growth must be slow 

 and feeble. It will also appear, that if lime do not 

 exist in the soil, but i'ew plants can find nourish- 

 ment; and that for the ripening of the seeds of 

 grain, phosphorus must be furnished also. The 

 latter substance may be absorbed in small quanti- 

 ties from the phosphuretted hydrogen, which is 

 occasionally present in the atmosphere; but a more 

 certain supply ousht to be sought in putrescent 

 manure, and particularly in that of animal ori- 

 gin. 



The uses of lime in agriculture, as will appear 

 from the foregoing remarks and the reasoning of 

 the essay, al-e as follows: 



1. When a soil contains inert animal or vege- 

 table matter, their decomposition may be promot- 

 ed, and it may be rendered fitfor'the food of plants, 

 by the addition of caustic lime. 



2. If the soil contain acid, that maybe neutral- 

 ized either by caustic or carbonated lime, and be- 

 sides, the organic matter whose decomposition 

 may have been prevented by the acid, will be per- 

 mitted to putrejy. 



3. Soils containing too much silica, or in other 

 words those which are sandy, are made more re- 

 tentive of moisture by the addhion of hme or its 

 carbonate. 



4. Clays, may be rendered less retentive of 

 moisture, and more friable by the same means. 



5. The gases which escape when vegetable or 

 animal matter putrefy, are retained in the soil by 

 means of lime or its carbonate ; and thus a given 

 quantity of manure, or the original vegetable mat- 

 ter of the soil, will retain its efficacy longer. By a 

 recent discovery, it has also been ascertained that 

 the decomposition of plants yields a peculiar acid, 

 called the humic, which forms Avilh lime a salt 



paringly soluble in water. The generation of this 

 salt also serves to render the nutriment contained 

 in the soil more lasting. 



6. Lime and its compounds are absolutely ne- 

 cessary, as constituent parts, to the growth of 

 many plants. The sulphate is essential to the 

 growth of clover, and the phosphate to that of 



