EARTHS. 



EARTHS. 



of it. Every plant is earth, and the growth and 

 true increase of a plant is the addition of more 

 earth." And in his chapter on the " Pasture of 

 Plants," Tull told his readers with great gravity, 

 that " this pasturage is the inner or internal 

 superficies of the earth ; or, which is the same 

 thing, it is the superficies of the pores, cavi- 

 ties, or interstices of the divided parts of the 

 earth, which are of two sorts, natural and arti- 

 ficial. The mouths or lacteals of roots take 

 their pabulum, being fine panicles of earth, 

 from the superficies of the pores or cavities, 

 wherein their roots are included." 



Tull wrote with all the enthusiasm of genius, 

 and carried his admiration of the powers of the 

 earth to support vegetation much too far ; he 

 was deceived, in fact, by the effects of his finely 

 pulverizing system of tillage, and did not suffi- 

 ciently attend to the fact, that there are many 

 other substances in the commonly cultivated 

 soils of the farmer besides the earths, and that 

 so far from their being always the chief con- 

 stituents of the soil, they very often form the 

 smallest portion of even a highly productive 

 field. 



That the four earths of which all cultivated 

 soils are composed are all the necessary food 

 or constituents of vegetables, has, long MIH-*' 

 Tull wrote, been decided by the accurate in- 

 vestigations of the chemist. Of these, lime, 

 either as a carbonate, or an acetate, or a sul- 

 phate, is by far the most generally pre^-nt in 

 plants; indeed, in one foim <>r another, it is 

 rarely absent from them. The presence of 

 silica (flint) is almost equally general. Mag- 

 nesia is less usually present, or, at least, it ex- 

 ists in smaller proportions ; and the same re- 

 mark applies to alumina (clay). 



The quantity of the earths which is present 

 in various vegetables is, therefore, a primary 

 question for the cultivator's guidance. This 

 will be seen from the following tables : 



Art*. 



1000 pans of the oak contain of the earths 1 030 



- beech 0453 



fir 0.003 

 Turkey wheat (Indian corn) 7-1 !<) 



sunflower 37:20 



vine branches 2-850 



box 2 674 



willow 2-515 



elm 1-flGO 



aspen T146 



fern 3'2'21 

 wormwood '2 HI 

 fumitory . 14000 



The proportions of the earths contained in 

 the commonly cultivated crops of the farmer 

 have been ascertained by M. Schraeder : this 

 able chemist obtained from thirty-two ounces 

 of the seeds of wheat (Triticum hybernum), of 

 rye (Secale cereale), barley (Hordeum n//^m), 

 oats (Jlvena saliva), and of rye-straw the fol- 

 lowing results : 



The earth silica or flint abounds in almost 

 every description of vegetable matter, espe- 

 cially in the grasses and Equisetum (horse-tail). 

 In the Dutch rush it is so plentiful that that 

 plant is used by the turner to polish wood, bone, 

 and even brass. It forms so considerable a 

 portion of the ashes of wheat-straw, that when, 

 these are exposed to the action of the blow- 

 pipe, it unites with the potash found also in the 

 straw, and forms an opaque glass. Davy found 

 I it most copiously in the epidermis or outer 

 bark of the plants he examined. 



Farts. 



100 parts of the epidermis of bonnet-cane contain 



of silica 90-0 



100 parts of the epidermis of bamboo-cane contain 



of silica 71'4 



100 parts of the epidermis of common reed contain 



of silica - 48'1 



100 parts of the epidermis of stalks of wheat con- 

 tain of silica - - - - - - 6-5 1 



In the joints of the bamboo a concrete sub- 

 slance is found, which Fourcroy and Vauque- 

 lin examined, and ascertained that it consists 

 of 70 parts of silica, and 30 parts of potassa. 

 This substance, which is named tabasheer, can 

 only be furnished by the soil. (Gehlen, vol. ii. 

 p. 112.) 



This earth, according to M.Saussure, consti- 

 tutes 3 per cent, of the ashes of the leaves of 

 oak gathered in May, 14-5 per cent, of those 

 gathered, in September, and 2 per cent, of the 

 wood. In the ashes obtained by burning the 

 wood of the poplar, it exists in the proportion 

 of 3-3 per cent.; of the hazel, 0'25 percent.; 

 of the mulberry, 0-12 percent.; of the horn- 

 beam, 0-12 per cent.; 0-5 per cent, in peas (Pi- 

 sum sativum) ; 61-5 in the straw of wheat ; 0-25 

 in the seeds ; 57-0 per cent in the chaff of bar- 

 ley; 35-5 in its seeds; and in the oat plant 60 

 pec cent. 



Lime is, if possible, still more generally 

 present in all plants than silica. "The salsola 

 soda," says Dr. Thomson, "is the only plant in 

 which we know for certain it does not exist.'* 

 (Sytt. of Chew. vol. iv. p. 190.) It is, however, 

 united with carbonic acid as carbonate of lime; 

 or it exists as the base of some other salt, 

 such as in oxalate of lime, or in sulphate of 

 lime (gypsum). It was found in the ashes re- 

 maining after the combustion of oak wood, at 

 the rate of 32 per cent., by M. Saussure. la 

 that of the poplar at the rate of 27 per cent. 

 He discovered also 8 per cent, in those from 

 the wood of the hazel ; 56 in those of the mul- 

 berry wood ; 26 in the hornbeam ; 14 in the 

 ripe plant of peas ; 1 per cent, in the straw of 

 the wheat, but not any in its seeds ; 12 in the 

 chaff of barley, but none in either its flour or 

 its bran ; neither did he find any in the oat 

 plant; but then, in the ashes of the leaves of 

 the fir (Pinus abies), raised on a limestone hill, 

 he found 43-5 per cent. 



Alumina, as I have elsewhere observed, is 

 found in most vegetables, but in much smaller 

 proportion than either silica or carbonate of 

 lime, and the same remark applies to magne- 

 sia. M. Schraeder found, as we have before 

 seen, in 2 Ibs. weight of the seeds of wheat 

 only T V ns of a grain of alumina, in rye l T 4 ff 

 grains, in barley 4 T 2 r grains, in oats 4 grains, 

 and in rye-straw 3 r 3 ,, grains. In 12 ounces of 

 wormwood there are about 5 grains of alu- 



429 



