158 



FARMERS' REGISTER— EXCRETIONS OF PLANTS. 



the venerable President of the Horticultural So- 

 ciety of London, that gentleman evinces his opin- 

 ion of the absolute novelty of the theory; thus, 

 "the continental naturalists have lately imagined 

 that trees emit some matter into the soil, of the 

 nature of excrement, which subsequently proves 

 noxious; but I do not assent to this o|)inion." 



What Brugmans ^stales is in accordance with 

 my theory, and with that now advocated by M. 

 De Candolle; in fact, I do not see how and in what 

 way we can by any possibility support, in all its 

 bearings, the theoiy of the rotation of crops, 

 otherwise than by that of the excretory power of 

 the roots of plants, and the consequent effects pro- 

 duced upon the soil. 



I shall now shortly explain what I mean by 

 ''the interchange between the fluids of the plants 

 and those of the so?7;" and then proceed to notice 

 particularly some of the leading facts stated in tlie 

 review of the new theoiy. . • 



I have throughout my work maintained .that the 

 vital powers of every living vegetable are stimu- 

 lated by the electrising principle of light; by the 

 agency of which, the nutritive substances being 

 about the radicals, are decomposed, and then at- 

 tracted and propelled into the recipient vessels of 

 the roots. The element so prepared, I consider 

 and designate the "fluids of the soil,'''' which, by 

 the same exciting energy, are, I conceive, carri- 

 ed upwards through the cellular sj^stem, till at 

 length they are deposited in the leaves, wherein 

 they are elaborated, and become the vital, nutri- 

 tive, j9ro/)er juices of the plant. These juices are 

 then, I argue, carried back from the leaves, and 

 distributed in due specific proportions, into cells or 

 vessels appropriated to every required function of 

 the plant; but certain portions are carried to and 

 through the roots, and propelled into the soil; not, 

 however, in the simple bland state of those taken 

 up by the vessels of supply, but imbued with pe- 

 culiar compound, odorous, and sapid qualities, the 

 effects of the process of elaboration within the 

 vessels of the leaves of the bark. These exuded 

 juices I style the 'fluids of the plant j'''' and as the 

 processes of supply and ascent, and those of return 

 and exusion, are unintermitting and coincident,— 

 the results of the same mighty electrising princi- 

 ple, — I view and describe them as acting inter- 

 changeably, as by the law of electric induction, 

 whatever is excited positively induces a negative 

 condition in a body immediately within the range 

 of its energy. It is evident that the vital princi- 

 ple stimulates the decomposition of the previously 

 inert matters of the soil about the roots of plants, 

 and that to a considerable distance, otherwise no 

 food could be introduced into the inconceivable 

 fine vessels of the fibrils. This food is pale, void 

 of taste or odor; whereas the prepared sap, which 

 distributes the nutritious matter to every part of 

 the vegetable, is frequently possessed of color, 



"Spongioles secrete excrem^ntitious matter, which 

 is unsuitable to the same species afterwards as food: 

 for poisonous substances are as fatal to the species that 

 secrete them, as to any other species." 



_ "But to other species the excrementitlous matter is 

 either not unsuitaWe, or not deleterious." 



"Hence, soil may be rendered impure, (or, as we 

 inaccurately say, worn out,) for one species, which 

 will not be impure for others." 



"This is the true key of \he theory of rotation of 

 crops." 



flavor, and scent, and these to a high degree in 

 many species; and the portion that is carried down 

 to the roots, is found to emit a peculiar and very 

 perceptible odor. 



In the present state of electrical science, it will 

 scarcely be denied that a subtile fluid pervades all 

 matter; that it is present in, and ])erhaps the ex- 

 citing agent of, all chemical action; and, moreover, 

 that it is the source of all the magnetic phenome- 

 na. "Will it then be deemed a mere play of the 

 fancy, to suppose that the whole of the processes of 

 the ascent of the raw sap, the elaboration of that 

 sap, its distribution, the exusion of a certain por- 

 tion of it, are specific electrical phenomena, pro- 

 duced almost instantaneously, and inducing one 

 another? I confess that I see no possibility of 

 otherwise accounting for the agency and effects of 

 vegetable vital action, unless, indeed, we consider 

 the vital ])rinciple of plants as res'embJing that of 

 the animal creation, and consequently as including 

 a sentient and discerning faculty, a power of voli- 

 tion and of choice ! 



Without dwelling upon an inquiry into the pre- 

 cise nature of vegetable vitalitj', I shall take it for 

 granted that the vital principle is stimulated by 

 external agency, and that all the functions of the 

 plant are at least excited by solar light and atmos- 

 pheric energy, whereby attractions are produced, 

 and decompositions effected, with regularity and 

 precision, and in an order that, is exactly suitable 

 to the constitution of each individual vegetable. 

 With this principle before me, I shall now revert 

 to the hypothesis of M. De Candolle, in connec- 

 tion with, and supported as it is by, the experi- 

 ments of M. Macaire. 



The former philosopher conceives that the true 

 theory of the rotation of «rops may be found iu 

 the fact, that plants exude more or less of excre- 

 mentitious matters from their roots; and M. Ma- 

 caire has followed up the idea by a variety of 

 chemical experiments, whereby he appears to 

 have ascertained that certain plants — one of which 

 was BIcrcuriaUs annua — took up, by the absorbent 

 powers of their roots, portions of acetate of lead 

 or of lime, which they again yielded to the distilled 

 water, in which the roots were subsequently im- 

 mersed; and that the fact was proved by chemical 

 reagents or tests best calculated to detect the small- 

 est portions of each of these substances. 



"The roots being partly placed in lime-water 

 and partly in pure water, the plant.? lived Avell, 

 and the pure water soon showed the presence of 

 lime by the oxalate of ammonia." Oxalate of 

 ammonia is readily prepared by dissolving a por- 

 tion — say one drachm — of carbonate of ammonia 

 in as much Avarm rain or distilled Avatcr as will 

 take it up in solution. Into this, a quantity of pure 

 oxalic acid dissolved in water is to be dropped, 

 till effervescence ceases, -when it maybe conchided 

 that a neutral salt is formed. This salt can he pro- 

 duced in crystals; but as this is not required for the 

 experiment in question, I shall not dwell upon it. 

 The saline neutral liquor being simply filtrated 

 through blotting-paper will amply suffice as a test; 

 and, indeed, it is one of the most subtile tests for 

 the presence of lime in solution that we possess; 

 perhaps one-hundredth part of a grain of lime in 

 a gallon or more of pure water would be detected 

 -by' it. 



With this reagent (and it is one of those which 

 every analyst of the eoil should possess himself 



