220 
THE CULTIVATOR. 
July 
RADICAL EXCRETION OF PLANTS. 
Sevens! years since the theory was first put forth by 
M. de Candolle, of Geneva, that “ plants possess the 
property of excreting by their roots substances which 
are formed in their lexture, and which, if retained 
in them, would be injurious to their healthy growth 
and development.” It was also contended by the 
same philosopher, that the excretions left in the soil 
by plants were injurious to the growth of succeeding 
crops of the same kind; and on this supposed fact, he 
based the expediency of a rotation in crops. 
M. de Candolle’s theory has for sometime been gene¬ 
rally regarded as unfounded; but as no particular ex¬ 
periments had demonstrated its truth or falsity, the 
Highland and Agricultural Society of Scotland offered a 
premium of twenty sovereigns in 1844, for the best 
essay on the subject based on practical trials and results. 
This premium was awarded to Mr. Alfred Gyde, who 
produced a highly interesting and valuable paper, 
which we find in the March number of the Transac¬ 
tions of the Highland Society. 
The points to which Mr. Gyde directed his inquiries, 
were as follows:— 
Do plants, or do they not, during their healthy growth 
excrete matter from their roots? 
If they excrete, is the matter excreted organic or 
inorganic? What is its composition? 
Does the matter excreted by different classes of plants 
possess properties peculiar to each class? If so what is 
the peculiar property of each? Is it identical with the 
sap of the plant, or does it differ? 
What is the physiological action of the roots of plants 
by which excretion takes place? 
Have plants the power of excreting by their roots, 
substances previously absorbed, and which are noxious 
to them? 
Will germination occur, and the growth of plants 
proceed, after the seeds have been impregnated with 
noxious matters? 
Will seeds germinate and grow in poisoned soils? 
Why do plants refuse to grow on some soils, while 
they grow freely on others? 
In order to grow the plants in such a manner that 
they could at any time be removed, and the roots sepa¬ 
rated from the soil without their being mutilated or 
broken, he adopted the following plan. The plants were 
grown 
1. In garden-soil, placed in pots, and plunged in the 
earth. 
2. In pots filled with silicious sand, the, growth of 
the plants being promoted by waterings with weak 
liquid manure. 
3. In pots filled with silicious sand which had been 
repeatedly washed in boiling water.'' 
4. In pots filled with damp moss. 
5. In pots filled with coarsely powdered charcoal. 
The plants grown were wheat, barley, oats, rye, 
vetches, kidney-beans, beans, peas, cabbages, mustard, 
and turneps. 
To ascertain whether matter is or is not excreted by 
the roots of plants, Mr. Gyde caused the plants to be 
removed from the pots in which they had grown, and 
had them carefully and thoroughly washed in a gentle 
stream of water ,— u after being carefully dried on folds 
of filtering paper, they were placed in glasses contain¬ 
ing distilled water, which had been exposed to the at¬ 
mosphere for some days. In this situation the roots 
were carefully excluded from the light, and kept at as 
uniform a temperatur#of about 55 degrees as practica¬ 
ble, the green portions of the plant Deing fully exposed 
to the action of light and air, the water in the vessels 
being renewed as it diminished, from absorption by 
the plant and evaporation from the surface. 
From several tables which are given, the particulars 
of the different experiments are seen. In relation to 
the results, Mr. Gyde observes: 
<e From the above experiment it will be seen that the 
roots of plants impart to water a portion of soluble 
matter or excretion, and that this excretion appears to 
be yielded in greater abundance by plants having large 
and spongy extremities to their roots, as beans, than 
by those possessed of fine, thread-like extremities, 
as is the case with wheat or cabbages. It will also 
be observed that in some instances the water has 
acquired an odor which is inseparable on the appli¬ 
cation of heat, and may be distilled over when the 
water is placed in a retort; the plants which impart 
odor to water, as the bean and cabbage, are also cha¬ 
racterized by emitting a similar odor from their leaves. 
Plants when in bloom were observed to emit a larger 
portion of excretion than when young or when ripen¬ 
ing their seeds; but the amount of excretion obtained 
even when many plants were operated upon, was very 
trifling, seldom more than a grain in weight when 
dry.” 
To ascertain whether the soil which had produced 
the plants contained any excretion, the following ex¬ 
periment was tried. 
“Sand, which had been well washed with boiling 
water was planted with beans ami peas; these plants 
were supplied with distilled water, and placed under the 
most favorable circumstances for healthy vegetation. 
After they had grown in the sand three weeks, they 
were removed, and the sand washed with distilled water, 
filtered, and on evaporation, yielded a portion of both 
organic and inorganic matter, in every respect similar 
to that obtained by the immersion of the roots in water. 
Plants of the same kinds to those used in the former 
experiments were cut from their stems, the lower ex¬ 
tremities of which were plunged in distilled w'ater, so 
that the descending sap, which it was presumed would 
escape, might be examined and compared with the 
radical excretions from the same kinds of plants, and it 
was found that in each instance similar results were 
obtained on evaporation of the water in which the cut 
plants had been immersed as those from the water in 
which the roots of similar plants had excreted. Hence 
we may conclude that the matter obtained from the 
roots of plants, or radical excretion, is similar to the 
sap of the plant from which it w r as excreted.” 
Mr. Gyde's observations in regard to the physiologi¬ 
cal action of the roots of plants, and the phenomena 
attending the circulation of the sap, are worthy particu¬ 
lar attention. 
“ The roots of plants are described as the downward 
prolongation of the stem, as the trunk and branches are 
the upward development into the air—the spongioles 
and extremities of the roots being the newest formed 
and extending portions, and that by these spongioles, 
fluids are taken up from the soil and conveyed to the cir¬ 
culation of the plants. 
“ The fluids thus absorbed are carried by the vessels 
of the most recently formed wood to the leaves, where, 
after undergoing certain changes during its exposure to 
the action of air and light, by which much water is 
given off by evaporation, the elaborated sap is returned 
by another set of vessels situated in the inner bark of 
the tree, to the roots, supplying during its descent, 
those constituents necessary for the healthy secretions 
of the plant. 
“ The sap having arrived in the roots, the new fluid is 
added to it from the soil, and the ascent again commences 
by the vessels of the new wood, this action continually 
taking place during the life of the tree, but progressing 
more rapidly at one season of the year than at another. 
« Many and ingenious are the theories which have 
been formed to explain the ascent of the sap. Of these, 
that which was first pointed out by Detrochet appears 
most probable, and is now generally received by phy¬ 
siologists. Detrochet found that if, into a glass tube, 
having one end covered with animal membrane tightly 
secured over it, a strong solution of salt in water or 
sugar in water be poured, and the end covered with 
membrane, be immersed in a vessel containing water- 
that within a few hours the liquid in the tube will be 
found to have risen several feet. This ascent of the liquid 
in the tube being caused by a portion of the water from 
the outside of the tube passing through the membrane 
and mixing with the solution in the tube; and at the same 
time a portion of the solution will be found mixed with 
