18 



HISTORY OF THE VEGETABLE KINGDOM. 



a similar experiment with a wheel, moviri!^ 

 horizontally, at the rate of one hundred and fifty 

 revolutions in the minute. The results were 

 similar, that is to say, aU the radicles were 

 directed towards the circumference, and the gem- 

 mules towards the centre; but with an inclina- 

 tion of ten degrees of the fonner towardjg the 

 earth, and of the latter towards the atmosphere. 

 These experiments were repeated by Dutrochet, 

 and with the same results, except that in the 

 second the inclination was not so considerable, 

 and that the radicles and gemmules.were nearly 

 horizontal. From these experiments, many 

 have concluded that the roots, in their descent, 

 merely obey the common laws of gravity. Be- 

 fore this conclusion could be made, however, the 

 phenomena of the gemmules ascending into the 

 air, contrary to the laws of gravity, ought to be 

 also explained. "But," says, Mr Keith, "if 

 gravitation acts so very powerfully upon tlie 

 radicle, why will it not condescend to exert 

 its influence upon the gemmules also, which, 

 if not so heavy as the radicle, are at least 

 specifically heavier than atmospheric air; and 

 why does it make an exception in favour of 

 some radicles." He then instances the case of 

 the misletoe. This singular plant shoots out 

 its radicle in whatever situation chance may 

 place it. Thus, when the seed, which is envel- 

 oped in a tliick and viscid glue, adheres to the 

 upper part of a branch, its radicle, which is a 

 kind of hoUow tubercle in the shape of a horn, 

 is then perpendicular to the horizon. If, on the 

 contrary, the seed be applied to the under sur- 

 faces of the branch, the radicle will be directed 

 towards the heavens; or if situated on the lateral 

 surfaces, the radicle will be directed laterally. 

 In short, in whatever situation the seed may be 

 placed upon the branch, the radicle will always 

 assume a direction perpendicular to its axis. 

 Dutrochet tried numerous experiments on the 

 germination of this seed, in order to ascertain 

 the laws of determination of its radicle. This 

 seed, which finds in the viscid substance that 

 surrounds it, the first materials of its growth, 

 germinates, and is developed, not only on wood, 

 either living or dead, but also on stone, glass, or 

 iron. Dutrochet caused it to germinate on a 

 cannon ball. In all these cases, the radicle was 

 invariably directed towards the centre of those 

 bodies. The same experimenter fastened a ger- 

 minating seed of misletoe to one end of a copper 

 needle, moving on a pivot like that of a marin- 

 er's compass, a small bit of wax being placed at 

 the opposite end, to serve as a counterpoise to 

 the seed. Matters being thus arranged, he 

 placed, ill a lateral direction to tlie radicle, a pin 

 of wood, so as to be at the distance of nearly half 

 a line. The whole was covered with a glass 

 receiver, so as to guard against disturbance from 

 external causes. After the lapse of five days, 



the stem of the embryo was bent, and its radicle 

 directed towards the small plate that was near 

 it, without any change being produced in the 

 position of the needle, notwithstanding its ex- 

 treme mobility on the pivot. Two days after, 

 the radicle was directed perpendicularly towards 

 the plate with which it came in contact without 

 producing the slightest derangement of the needle 

 that bore the seed. The radicle of this seed 

 exliibits another constant tendency, which is that 

 of avoiding light. If the seeds are made to ger- 

 minate in the inner side of the glass of a window, 

 the radicles are aU directed to the interior of the 

 apartment in search of darkness. If a seed be 

 stuck on the outside of the glass, the radicles 

 closely adhere to it, impelled by its tendencies 

 inwards to shun the light. These, and other 

 facts, then, present unsurmountable objections to 

 the theory of mere mechanical attraction. "If," 

 says Mr Keith, "I were to offer a conjecture in 

 addition to the many that have been already 

 formed, I should say that the invincible tendency 

 of the radicle to fix itself in the earth, or other 

 proper soil, and of the gommule to ascend into 

 the air, arises from a power inherent in the 

 vegetable subject, analogous to what we caU in- 

 stinct (or, perhaps, he should have said the vital 

 impulse) in the animal, infallibly directing it 

 to the situation best suited to the acijuisition of 

 nutriment, and consequent developement of its 

 parts. And upon this hypothesis, we include 

 aU varieties of plants whatever, parasitical as 

 well as others. For let them attach themselves 

 to whatever substance they will, to them it still 

 affords a fit and proper soil." Something more 

 than mechanical attraction is evident also in the 

 tendrils of climbing plants ; one species uniformly 

 twisting to the right, while another as constantly 

 twists to the left. The explanation of Dutrochet's 

 theory of the ascent of sap, to be given after- 

 wards, will perhaps tend to throw some light on 

 this curious subject. 



Economical uses of roots. Many roots are use- 

 fully employed in domestic economy, as articles 

 of food. Such ai'e the well known roots of 

 carrots, turnips, parsnips. These have been 

 greatly increased in size by cultivation, so much 

 so as scarcely to be known to be the same as the 

 original species growing wild. From the tuber- 

 cles of the orchis tribe, salop is manufactured ; 

 sugar is got from beet root, of a quality little 

 inferior to that obtained from the cane. Roots 

 are more generally odorous than the stems of 

 plants, which is owing to an essential oil. Thus, 

 ginger, horse radish, valerian, spignel, and sweet 

 cicely, are pungent and aromatic ; the root of 

 white hellebore is bitter and nauseous. Other 

 roots again are sweet, bland, and mucilaginous, 

 as liquorice root, beet, caiTot, &c. Some roots 

 are used for dyeing, as madder, alkanet, turmeric ; 

 other roots are medicinal, as rhubarb, ipeca- 



