6 1 8 Ijondon Hoiti cultural Society and Garden. 



Vegetables and Animals ; IMerioration of Soil in u'liich Plants of the same 

 Kind have ^rown for a lonsi Period ; Poisons ; Excretions ; Nature of 

 the Sap ; (>r^ans of Respiration ; Cause of Circulation ; Antediluvian 

 Plants. — Tlic i)rofc'.ssor first observed tliat every one who had at all lon- 

 siilered the subject must be struck with the remarkable analogy which 

 exists between the blood of animals and the sap of plants. Both supply 

 nourishment, and are indeed essentially necessary to the developcment 

 and support of the vital principle; but both require to be elaborated by 

 circulation before they become fully imbued with their nutritious (jualities. 

 Sap, when first absorbed by the roots, is simply water, impregnated with 

 various extraneous substances, derived either from the soil or froin acci- 

 dental circumstances. These substances, some of which are useful and 

 some injurious to vegetation, are absorbed by the plant indiscriminately; 

 the spongioles having no power of selection, but being naturally inclined 

 to take up wiiatever moisture they can find. The vulgar notion that plants 

 deteriorate if grown too long on the same soil, because they have exhausted 

 all the juices wholesome for them which it contains, is, therefore, mani- 

 festly erroneous. That tiiey do deteriorate is true, but the cause is different. 

 The fact that plants will absorb any moisture presented to them has been 

 proved by various experiments ; in the course of which they have been 

 forced to take up coloured fluids, and even poisons, which have produced 

 derangement of the ordinary functions, and freijucntly death. The cir- 

 cumstance that the same poisons act nearl\ in the same manner on vege- 

 tables and animals is another curious proof of analogy between them. All 

 poisons are either corrosive or narcotic ; or, in other words, act either by 

 ovcr-stinuilating or by relaxing the system ; ami these different effects 

 have been shown clearly, by various experiments, to be producible on 

 plants. One branch of the common berl)erry was steeped in a solution 

 of corrosive sublimate, and another in a decoction of opium ; when, in 

 a short time, the vessels of the one were founil to have become turgid, 

 and of the other relaxed, the natural irritability of the plant being, in both 

 cases, destro3ed. The fact that plants absorb acjueous jiarticles imliscri- 

 minately, being thus [)roved, it is clear that they cannot exhaust any soil 

 by abstracting its nutritious (|ualities, and that the deterioration which 

 takes place in the soil, where the same kind of plant has been grown for 

 any length of time, nnist arise from some other cause. This cause is the 

 excretions thrown ofi" by tlic plant, which, in progress of time, literally 

 poison the soil. 



The moisture absorbed by the spongioles having ascended to the leaves, 

 and been elaborated there into sap, returns, depositing, by the way, all the 

 nutritious particles it has acquired ; and at last throws off the residuum, 

 in the shape of a s[K)ngy excrescence, at tiie root. These excretions, con- 

 sisting only of what the plant has rejected, are of course unfit for the 

 support of other plants of a similar nature, and may be said to poison 

 the soil. The extraordinary ])ower possessed by plants, of getting rid of 

 injurious substances, has i)een shown by placing one half of the roots of 

 a plant in a vessel containing jjure water, ami the other half in a solution 

 of acetate of leail ; when, in a few days, the water was fouml strongly impreg- 

 nated with the poison. Many other experiments have been trieil, but they 

 have always been attended with a similar result. Botanists, observing these 

 facts, have sometimes applied them practically; and, instead of transplant- 

 ing trees with a ball of earth adhering to their roots, or repotting plants 

 by merely putting fresh earth round the mass of fibrils formed in the 

 former pot, have carefiilly washed the roots from every particle of their 

 former soil, before placing them in their new situations. Among the re- 

 markable circumstances attending the effects of [loisons on plants, it may 

 l)c observed that a decoction of a poisonous plant will kill a plant of a 



