[page] 489

I. Roots

THE observations which led to the first of these papers were originally made many years ago on Euphorbia peplus, and have now been extended to other genera. A plant of E. peplus having been dug up and carefully washed, the smaller rootlets may be placed under the microscope without further preparation, the thicker roots may be examined by means of sections. If such roots are left, before being examined, in a solution of carbonate of ammonia (1 to 7 per 1000) for a short time (varying from a few minutes to several hours), they present a wonderfully changed appearance. The most striking alteration is that the surface of the root assumes a longitudinally striped appearance, due to longitudinal rows of darker brown cells, alternating with lighter coloured rows. The darker colour is seen under a high power to be due to the presence of innumerable rounded granules of a brown tint, which the lighter-coloured cells are without. Similar brown granules are deposited in cells scattered throughout the parenchyma, and markedly in the elongated endoderm cells surrounding the vascular bundle.

The granules are apparently neither resinous nor fatty, for they are not removed by alcohol or ether; they axe, Abstract by Mr. Francis Darwin of two papers by Mr Charles Darwin read before the Linnean Society on March 16.

[page] 490

however, slowly acted on by caustic potash, and seem to be of the nature of protein.

It will be observed that the most remarkable part of the phenomenon is that the granules are only formed in some of the external cells, and that these cells are, before the treatment with ammonia, indistinguishable in shape or by their contents from their fellows, which are unaffected by the solution.

There is, however, a curious functional difference between the two classes of cells, namely, that the granular cells do not produce root-hairs, which arise exclusively from the cells of the light-coloured rows. With this fact may be compared an observation of Pfeffer's, that the root-hairs of the gemmæ of Marchantia grow only from certain definite cells. He describes a similar state of things in Hydrocharis, but with these exceptions it seems not to have been hitherto suspected that root-hairs arose from cells in any way specialised.

In connection with this fact, the theory suggests itself that the light-coloured cells have been emptied in consequence of the granules having been used up in the development of the root-hairs. But this view is not compatible with the fact that light-coloured cells may often be found which have not produced root-hairs. Again, in the case of Cyclamen, root-hairs are produced from granular cells. Effects similar to those now described were observed in some other Euphorbiacious plants, e.g. Phyllanthus compressus, though not in all the genera of this family which were observed. Among genera belonging to other families may be mentioned Drosophyllum and Cyclamen, as showing the phenomenon especially well. Altogether 49 genera were observed; of these 15 were conspicuously acted on, and 11 in a slight degree, making together 26 genera, while the roots of the remaining 23 genera were not acted on in any plain manner.

Before attempting to draw any conclusions, a few more details must be taken into account. The root must be alive, otherwise no precipitation will take place; the process is therefore a vital one, and seems in some measure to resemble "aggregation," as it occurs in the tentacles of Drosera. In both cases carbonate of ammonia is the most efficient re-agent, but other salts, such as nitrate of ammonia, produce a similar effect. What the nature of the process may be, must remain doubtful. The view here suggested is that the granular matter is of the nature of an excretion; the arrangement of the dark-coloured cells in rows agrees with what we know of the disposition of certain cells whose function is admittedly to contain excretions. The granules are, moreover, deposited in the loose exfoliating cells of the root-cap where they cannot take part in the life of the root; and this fact points in the same direction.

2. On the Action of Carbonate of Ammonia on Chlorophyll Bodies. –The effects of solutions of carbonate of ammonia and of other fluids on the tentacles of Drosera, &c., was described in "Insectivorous Plants,"' under the name of "aggregation." This process consists essentially in the appearance of curiously-shaped masses, of an albuminoid nature, which undergo striking changes of form. The masses were believed to be protoplasmic, but this conclusion has not been generally accepted, and has been called in question by such authorities as Cohn and

Pfeffer. The present paper is intended to show that carbonate of ammonia causes a kind of aggregation in chlorophyll bodies; and as these are undoubtedly protoplasmic, the belief in the protoplasmic nature of the aggregated masses in Drosera, and other carnivorous plants, is supported.

The changes which occur in the chlorophyll bodies may be well observed in the case of Dionaea. If a young leaf is immersed for twenty-four hours in a solution of carbonate of ammonia (7 to 1000), and is then examined by making thin sections, the contrast with a normal leaf will be found strikingly great. In most of the cells, not a single chlorophyll-grain can be seen, but in their place are found masses of translucent yellowish-green matter of diversified shapes, resembling in a general way the aggregated masses in the tentacles of Drosera. The matter is not exclusively derived from the chlorophyll grains, but consists, in part, of matter deposited from the cell-sap, which is often the first to be formed, and is afterwards surrounded by the green matter derived from the chlorophyll-grains.

The same process may be observed in Drosera, and here it is not necessary to make sections, as the chlorophyll-grains may be well seen at the bases of the tentacles. Many observations were made in this way, and also by means of sections. ln the case of Drosera it was possible to show that the chlorophyll-grains may recover from the effects of the carbonate-and this is a fact of some importance. After placing drops of various solutions on the discs of leaves still attached to their plants, green spheres or green zones surrounding a central purple mass were to be found in the tentacles. In this case it will be seen that the chlorophyll grains join with the purple cell-contents in forming aggregated masses. These masses were observed to be in constant slow movement. The leaves were then syringed with water and left to themselves for some days. When again examined, the green spheres had in large part disappeared, and instead of them normal chlorophyll-grains were found.

Other observations were made on Drosophyllum, Sarracenia, Primula sinensis, Dipsacus, Pelargonium, Cyclamen, and many other genera, with various results.

In some cases the chlorophyll-grains disappeared, and the green masses were formed, in other cases hardly any effect was produced; in others again the chlorophyll-grains became confluent and formed curious horse-shoe like masses in the bottoms of the cells.

In the case of Spirogyra the effects of the carbonate were well marked, the spiral chlorophyll body breaking up into variously formed rounded and pear-shaped masses, which slowly changed their outline. Here also plainly-marked deposition of fine granular matter from the cell-sap was caused by the ammonia solution.

Finally, it may be pointed out that whether or not the argument from the facts here given in favour of the protoplasmic nature of the aggregates in Drosera be considered valid, the observations themselves possess some independent interest.