618 London Horticultural Society and Garden. 



Vegetables and A?iimals ; Deterioration of Soil in which Plants of the same 

 Kind have grown for a long Period ; Poisons ; Excretions ; Nature of 

 the Sap ; Organs of Respiration ; Cause of Circulation ; Antediluvian 

 Plants. — The professor first observed that every one who had at all con- 

 sidered 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 developement 

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

 circulation before they become fully imbued with their nutritious qualities. 

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

 various extraneous substances, derived either from the soil or from 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 whatever 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 they 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 frequently death. The cir- 

 cumstance that the same poisons act nearly 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 

 over-stimulating or by relaxing the system; and these different effects 

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

 plants. One branch of the common berberry 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 found to have become turgid, 

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

 cases, destroyed. The fact that plants absorb aqueous particles indiscri- 

 minately, being thus proved, it is clear that they cannot exhaust any soil 

 by abstracting its nutritious qualities, and that the deterioration which 

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

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

 excretions thrown off by the 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 spongy excrescence, at the 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 power possessed by plants, of getting rid of 

 injurious substances, has been shown by placing one half of the roots of 

 a plant in a vessel containing pure water, and the other half in a solution 

 of acetate of lead ; when, in a few days, the water was found strongly impreg- 

 nated with the poison. Many other experiments have been tried, 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 carefully 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 poisons on plants, it may 

 be observed that a decoction of a poisonous plant will kill a plant of a 



