428 



FARMERS' REGISTER, 



[No. 7 



enable them to digest the crude matter which they 

 obtniii from the soil. 



''The fixing of carbon by the action of light 

 contributes in an eminent dsgree to the quality of 

 timber; a point of no small importance in all 

 countries. It is in a great degree to the carbon in- 

 corporated with the tissue, either in its own pro- 

 per ibrm, or in combination with other elements, 

 in the form of resinous or astringent matter, tlinf 

 dilierence in quality in t!ie timber of the san)e 

 species of tree is principally owing. Isolated oak 

 trees, fully exposed to the influence of light, b3- 

 come a tougher and more durable timber, than 

 the same species growing in dense forests; in the 

 Jormer case its tissue has been solidified by the 

 greater quantity of carbon fixed in the system 

 during its growth. There is every reason to be- 

 lieve "^that the brittle wainscot oak of the Black 

 Furest, Eng. is produced by the very same spe- 

 cies as the solid naval timber of Great Britain. " 

 The results of clieuiical analysis confirm this opi- 

 nion, as will be seen by noticing the quantity ol 

 carbon obtained form diHerenl kinds of wood, as 

 given in the following table. 



Cormonna-wood - 55 per cent of carbon. 



Iron-wood - - 53.44 " 



Oak - - - 52.50 " 



Beech - - - 51.45 " 



Box - - - 50 " 



Willow - - 49.80 " 



'•It is to the power which sun-light possesses of 

 decomposing carbonic acid, and fixing the carbon 

 in the tissues of the plant, that the direction 

 which the branches of a tree assume, is generally 

 to be ascribed. When a branch first protrudes 

 from a stem, its own weight would bend it down- 

 wards, if it were not fir the efiects of light from 

 above, which solidifies the pan exposed to it. Let 

 any one expose a green branch in such a way that 

 liifht strikes it only on one side; the tissue on that 

 side will fix the most carbon, will become harder 

 and lengthen less; while the tissue of the oppo- 

 site side, fixing less carbon, will liarden less, and 

 lengthen more; the consequence of which will be 

 that the branch will be eventually turned towards 

 the light. This will explain the uniform tendency 

 of the trreen parts of plants to turn towards the 

 light." ^ 

 "Besides fixing simple carbon in the tissues of a 

 plant, light appears to exert a very important and 

 necessary agency in the production of many of 

 the proximate principles of vegetables. Of its in- 

 fluence in the production of the various kinds of 

 coloring matter, and also, of the odoriferous prin- 

 ciples, 1 have already spoken, when treating of 

 those subjects. To the formation of starch, a 

 substance into the composition of which carbon 

 enters very largely, sun-light appears to be ne- 

 cessary. It is to the starch which they contain, 

 that potatoes, corn, and many other plants, owe 

 most of their nutritive properties. Potatoes grown 

 in the dark, are always watery, in consequence o. 

 no starch being developed in them; and indeed 

 the quantity of^ nutritive matter which they con- 

 tarn, is, in other circumstances, proportioned to the 

 intensity of the light to which their leaves, (the 

 orsans in which the elaboration of the sap is 

 principally effected,) are exposed. When or- 

 chard-ground is undercropped with potatoes, the 

 quality of the potatoes is never good, simply be- 



cause eo large a quantity of light is intercepted by 

 the leaves and branches of the orchard-trees, as 

 to retard the formation of starch. The formation 

 of the milky juices of many plants, appears to de- 

 pend upon the presence of solar light. As these 

 milky juices are (i^equently poisonous, it is a mat- 

 ter ot' crreat importance to prevent their formation, 

 where the plant is intended to be eaten. Hence 

 the common practice of blanching, as it is called; 

 which is in fict nothing more than excluding the 

 sun-light from the plant, to prevent the formation 

 of certain substances vvhicii would have been 

 formed, had sun-liglit had free access to the plant. 

 Hence too, the safety with which the young 

 shoots, which have but just protruded from be- 

 neath the ground, are eaten, when the same plant 

 if eaten at any subsequent period of its growth^ 

 u'ould have been highly deleterious. 



Another of those facts which the practical ag- 

 riculturist should bear in mind, is that tempera- 

 ture has grpat influence over the elaboration of 

 sap. The agency which heat exerts in this pro- 

 cess, is no doubt, to be attributed principally to the 

 evaporation of watery fluids from the crude sap, 

 which it necessarily causes. It has long been 

 known that a very large portion of (he water 

 which is absorbed by a plant is afterwards lost 

 again by evaporation. Indeed such it will at once 

 appear, must be the case, if we call to mind the 

 liict, that ail the solid components of vegetables 

 must enter them in solution of water, and that 

 many of those solids are soluble to but a very 

 small extent, in that fluid. It is possible, perhaps 

 we might say probable, that heat also exerts a di- 

 rect agency in causing combinations among the 

 elementary substances, of which plants are com- 

 posed. There is no known agency which is more 

 powerful than that of heat, in effecting changes 

 in the chemical relations of bodies; hence it is that 

 the chemist, in almost every operation, depends 

 upon its assistance. When we know that heat 

 does exert so powerful and so universal an influ- 

 ence as this, in those chemical operations which 

 are effected by the art of man, it would seem but 

 a reasonable inference, that nature also would 

 make use of it, in those more complicated, and as 

 they seem to us, more mysterious operations, which 

 art may in vain attempt to imitate. 



But in whatever way heat may affect the vital 

 action of plants, it is certainly true, and every 

 one's observation will convince him of the fact, 

 that it does exert a powerful influence over those 

 vital actions. It is only when the temperature of 

 the air is raised sufficiently high, that the vital en- 

 ergy of a plant is excited. Although light is ne- 

 cessary to perfect the growth of a plant, and to 

 the formation of many of those proximate princi- 

 ples which plants contain, yet if a plant be ex- 

 posed to an elevated temperature, tliough it be in 

 total darkness, that developement of its parts and 

 consequent increase in size which we denominate 

 growth, will certainly take place. The influence 

 of heat appears to be exerted immediately upon 

 the stem and leaves, and through them, upon the 

 root. Hence it is, that vvhen one branch of a vine 

 growing in the open air, is introduced into a hot- 

 house, the temperature of the hot-house excites the 

 buds into action; they immediately attract fluids 

 from beneath them, and thus the whole system 

 is put in motion, although the parts of the vine- 

 plant beyond the house, are exposed to all the in- 



