OF AMMONIA ON THE ROOTS OF PLANTS. 259 
while those of the remaining 23 genera were not affeeted, at least 
in any plain manner. But it should be stated that sections of 
all these latter roots were not made, so that the cells of the 
parenchyma and endoderm were not examined. We may there- 
fore suspect that if various other reagents had been tried, aud if 
sections had been made of all, some effect would have been ob- 
served in a larger proportional number of cases than actually 
oecurred. I have elsewhere shown that the contents of the 
glandular hairs and of the epidermic and other cells of the leaves 
undergo aggregation in a considerable number of plants when 
they are acted on by carbonate of ammonia; and the roots of 
these same plants are especially liable to be affected in the same 
manner. We see this in 7 out of the 15 genera which had their 
roots conspicuously affected coming under both heads. 
The question naturally arises, what is the meaning of matter 
being precipitated by a solution of carbonate of ammonia and of 
some other substances in certain cells and not in other cells of 
the same homologous nature? The fact of granules and sphe- 
rical masses being formed within the loose exfoliating cells of the 
root-cap, as was observed in several instances, and conspicuously 
in that of Drosophyllum, apparently indicates that such matter 
is no longer of any use to the plant, and is of the nature of an 
excretion. It does not, however, follow that all the aggregated 
matter within the root-cells is of this nature, though the greater 
part may be; and we know that in the filaments of Spirogyra not 
only are granules deposited from the cell-sap which aggregate 
into spheres, but that the spiral chlorophyll-bands also contract 
into spherieal or oval masses. The view that the granules con- 
sist of excreted matter is supported, to a certain extent, by their 
not being redissolved, as far as I could judge, in the roots of 
living plants of Euphorbia Peplus ; and in this respect they differ 
in a marked manner from the aggregated matter in the leaves of 
Drosera and its allies. A larger amount of granular matter is 
deposited close to the tip of the root than elsewhere; and it 
might have been expected that where growth with the accom- 
panying chemical changes was most rapid, there the largest 
amount of excreted matter would accumulate. It also deserves 
notice that there exists some degree of antagonism between the 
presence of these granules and of starch-grains in the same cells. 
On the other hand, it must be admitted that no excretion in the 
vegetable kingdom, as far as is at present known, remains dis- 
