EXCRETION OF PLAITTS. 



ON THE EXCRETION OF PLANTS. 



BY THOMAS MEEHAN, QAEDENER TO CALEB COPE, PHILADELPHIA. 



Every person connected with the cultivation of the soil is aware that soils wear out, 

 or become exhausted, by being constantly cropped with one kind of plant. It has 

 been supposed by many, that the soil under such circumstances becomes impover- 

 ished by the plants. Others, again, conclude that it is poisoned by excrements 

 thrown off by the roots. I propose to examine the arguments advanced by the latter, 

 not with the object of showing that the soil may not be deteriorated by the excre- 

 ments alluded to, but that they have hitherto failed to prove even the probability of 

 the hypothesis. 



It seems to be admitted that plants excrete indigestible matter from their roots. 

 " The roots not only absorb fluid from the soil, but they return a portion of their 

 peculiar secretions back again into it, as has been found by Brugmans, who ascer- 

 tained that some plants exude an acid fluid from their spongioles ; and also by Mr. 

 Macare, who has proved that to excrete superabundant matter from the roots, is a 

 general property of the vegetable kingdom." — (^Lindley, In. £ot., Book, II, Chap. 2.) 

 " If we place a growing bulb in a vessel of water, but do not change the water, in a 

 few days a slimy substance appears in the water, evidently an excretion from the 

 roots." — {Horticulturist, Vol. VII, p. 507.) " If you place a succory in water, it 

 will be found that the roots will by degrees render the water bitter, as if opium had 

 been mixed with it ; a spurge will render it acrid ; and a leguminous plant mucilagi- 

 nous. And if you poison one half of the roots of any plant, the other half will throw 

 the poison off again from the system." — {Theory of Horticulture, par. 40.) "An 

 apple orchard will not immediately succeed upon the site of an old orchard of the 

 same kind of fruit. No amout of manuring will enable it to succeed. Dahlias do 

 not 'like' the soil in which dahlias grew last year." — {Ibid., p. 284.) 



All the extracts, except the last, show that plants do excrete from the roots certain 

 substances. The last extract is one of many observations which have been recorded 

 to show that successive cropping deteriorates soil. That there is some change in it, is 

 undoubted ; but that it is caused by their excrements, is assumed. We know that 

 each individual plant absorbs from the soil peculiar elements ; or, at least, peculiar 

 proportions of various elements. This has been proved by chemical analysis. Have 

 the excrements of any given plant been subjected to the same ordeal, and the nature 

 of the assumed poison been detected ? "Would it prove to be arsenic, opium, or any 

 of the metallic or alkaline poisons that are known to be as destructive to vegetable as 

 to animal life ? Whether with the idea of showing the injurious effects of excremen- 

 titious matter or not, such an analysis would be highly interesting to those who culti- 

 vate the soil. The idea that it injures the soil, seems to originate from the apparent 

 impossibility of a plant taking up again what it has once thrown off. But has it been 

 proved that the matter thus thrown oft" must necessarily remain unaltered in the 

 soil, and may not be immediately changed, by conjunction or chemical affinity 



