VEGETABLE CHEMISTRY. 



grain in strata a few inches thick, on large, airy, 

 but shaded floors, where it remains for about 

 twelve or fourteen days, until germination has ad- 

 vuiced to the extent desired by the maltster. Dur- 

 ing this interval, the grain is frequently turned, in 

 order that the temperature of the whole mass may 

 be uniform. As soon as saccharine matter is freely 

 developed, germination must be arrested ; since, 

 otherwise, being taken up as nutriment for the 

 voting plant, it would speedily disappear. Accord- 

 ingly, the grain is removed to the kiln, where it is 

 exposed to a temperature gradually rising from 100 

 to 160, or rather higher ; the object being first to 

 dry the grain completely, and then to provide 

 against any recurrence of germination, by destroy- 

 ing the vitality of the plant. The difference be- 

 tween malted and unmalted barley is readily per- 

 ceived by the taste ; but it will be more correctly 

 appreciated by inspecting tbe result of a compara- 

 tive analysis of the two. 



Resin, . 

 Gum. . 

 Suw, . 



(.liit.-ii, 

 Starch, 

 lii.r.li-in. 



1 



4 



6 



3 



32 



55 



In inn of 

 M*lt. 



. I 



15 



. 15 



1 



. 56 



12 



It hence appears, that, during germination, the 

 hordein is converted into starch, gum and sugar ; 

 so that, from an insoluble material, which could 

 not, in that state, be applied to the uses of the 

 young plant, two* soluble and highly nutritious 

 principles result, which, by being dissolved in water, 

 are readily absorbed by the radicle. In the growth 

 of plants, a striking analogy to that of animals is 

 noticeable. The root serves the purpose of a 

 stomach, by imbibing nutritious juices from the 

 soil, and thus supplying the plant with materials 

 for its growth. The sap, or circulating fluid, com- 

 posed of water, holding in solution saline, extrac- 

 tive, mucilaginous, saccharine, and other substances, 

 rises upwards through the wood in a distinct system 

 of tubes, called the common vessels, which corre- 

 spond in their office to the lacteals and pulmonary 

 arteries of animals, and are distributed in minute 

 ramifications over the surface of the leaves. In its 

 passage through this organ, which may be termed 

 the lungs of plants, the sap is fully exposed to the 

 agency of light and air, experiences a change, by 

 which it is more fully adapted to the wants of the 

 vegetable economy, and then descends through the 

 inner layer of the bark in another system of tubes, 

 called the proper vessels, yielding, in its course, all 

 the juices and principles peculiar to the plant. 

 Plants absorb carbonic acid from the air, under 

 certain circumstances, and emit oxygen in return. 

 When a healthy plant, the roots of which are sup- 

 plied with proper nourishment, is exposed to the 

 direct solar beams in a given quantity of atmospheric 

 air, the carbonic acid, after a certain interval is re- 

 moved, and an equal volume of oxygen is substituted 

 for it. If a fresh portion of carbonic acid is supplied, 

 the same result will ensue. But t'his change only 

 takes place in the sunshine: in the dark, an opposite 

 effect takes place ; oxygen disappears, and carbonic 

 acid is evolved. In the dark, therefore, vegetables 

 deteriorate rather than purify the air, producing the 

 same effect as the respiration of animals. Plants 

 appear to derive a large proportion of their carbon 

 from the carbonic acid of the atmosphere. Light is 

 necessary to the colour of plants. The green co- 

 lour of the leaves is not developed, except when 



they are in a situation to absorb carbonic acid, au;l 

 give out oxygen. With respect to the food of 

 plants, the chief source from which plants derive 

 the materials for their growth, is the soil. How- 

 ever various the composition of the soil, it consists, 

 essentially, of two parts, so far as its solid consti- 

 tuents are concerned. One is a certain quantity of 

 earthy matters, such as siliceous earth, clay, lime, 

 and sometimes magnesia ; and the other is formed 

 from the remains of animal and vegetable substances, 

 which, when mixed with the former, constitute 

 common mould. A mixture of this kind, moistened 

 by rain, affords the proper nourishment of plants. 

 The water, percolating through the mould, dissolves 

 the soluble salts with which it comes in contact, 

 together with the gaseous, extractive, and other 

 matters, which are formed during the decomposition 

 of tbe animal and vegetable remains. In this state 

 it is readily absorbed by the roots, and conveyed as 

 sap to the leaves, where it undergoes a process of 

 assimilation. But, though this is the natural pro- 

 cess by which plants obtain the greater part of their 

 nourishment, and without which they do not arrive 

 at perfect maturity, they may live, grow, and even 

 increase in weight, when wholly deprived of nutri- 

 tion from this source. Thus it is well known, 

 that many plants grow when merely suspended in 

 the air. Without water, plants speedily wither 

 and die. It gives the soft parts that degree of 

 succulence necessary for the performance of their 

 functions ; it affords two elements, oxygen and hy- 

 drogen, which, either as water, or under some other 

 form, are contained in all vegetable products ; and 

 lastly, the roots absorb from the soil those sub- 

 stances only which are dissolved or suspended in 

 water. So carefully, indeed, has nature provided 

 against the chance of deficient moisture, that the 

 leaves are endowed with a property both of absorb- 

 ing aqueous vapour directly from the atmosphere, 

 and of lowering their temperature during the night 

 by radiation, so as to cause a deposition of dew upon 

 their surface, in consequence of which, during the 

 driest seasons, and in the warmest climates, they 

 frequently continue to convey this fluid to the 

 plant, when it can no longer be obtained in suffi- 

 cient quantity from the soil. But, necessary as is 

 this fluid to vegetable life, it cannot yield to plants 

 a principle which it does not possess. The carbon- 

 aceous matter which accumulates in plants, under 

 the circumstances above alluded to, may with cer- 

 tainty be attributed to the atmosphere, since we 

 know that carbonic acid exists there, and that 

 growing vegetables have the property of taking 

 carbon from that gas. When plants are incinerated, 

 their ashes are found to contain saline and earthy 

 matters, the elements of which, if not the com- 

 pounds themselves, are supposed to be derived from 

 the soil. Such, at least, is the view deducible from 

 accurate researches and from chemical principles. 

 Some later experiments, however, would seem to 

 lead to a different conclusion. Several kinds of 

 grain, such as barley, wheat, rye and oats, in pure 

 flowers of sulphur, were supplied with nothing but 

 air, light, and distilled water ; on incinerating the 

 plants thus treated, they yielded a greater quantity 

 of saline and earthy matters than were originally 

 present in the seeds. These results may be ac- 

 counted for in two ways. It may be supposed, in 

 the first place, that the foreign matters were intro- 

 duced accidentally from extraneous sources, as by 

 fine particles of dust floating in the atmosphere ; 

 or, secondly, it may be conceived, that they were 



