description of tissue that the phenomenon of cyclosis takes place. The detailed statements of Professor Schultz of Berlin, to whom, almost exclusively, we owe all that we know with precision concerning this important discovery, were communicated to the Academy of Sciences of Paris, in September, 1829; they were reported upon in September, 1830, by Messrs. Cassini and Mirbel, with a recommendation that the memoir, and the beautiful drawings accompanying it, should be published. This, however, was not done, but, in the year 1833, the great Montyon prize in physics was awarded to M. Schultz, for a new memoir upon cyclosis, upon the report of Messrs. Auguste de St. Hilaire, Dutrochet, Adr. de Jussieu, Becquerel, and De Mirbel. Owing, however, to some unexplained cause, the memoir is still, March, 1839, unpublished, although its appearance is said to be close at hand. Under these disadvantageous circumstances, it is not surprising that so many errors should have been committed concerning cyclosis: some, among whom I am to be numbered, doubting its existence as a peculiar system of motion; most writers confounding it with rotation; and a few describing it, but, according to its discoverer, with but little attention to precision. I confess that, until I enjoyed the advantage of examining it with Professor Morren and Professor Schultz himself, I had no exact ideas concerning it. In the following statement, I have endeavoured to confine myself to the explanations given by Professor Schultz himself, with one or two exceptions.

1. The phenomenon of cyclosis consists of a motion of fluid called latex, usually more or less milky, but often transparent, which conveys granular matter through a plexus of reticulated vessels, in all directions; when the vessels are parallel and near each other, the currents rise in some and fall in others, but, in connecting or lateral vessels, the currents are directed from right to left, or the reverse, according to no apparent rule. The contiguous rows of vessels anastomose from place to place; which produces a permanent interruption of the rising and falling currents. In order to enable a circulating motion to take place, it is necessary that the system of vessels should be reticulated, as takes place in the

peripherical vascular system of animals. The vessels contract and become so small as to be invisible, they then fill themselves again, enlarge, and re-establish the communication which had been interrupted. It often happens that when strong currents are formed, the weak ones disappear. If a current is about to stop, it may be seen to oscillate a moment both in front and rear. If the globules are amassed in a particular place, an obstruction takes place, and the fluid part of the latex is no longer capable of passing along. If we take a thin slice of bark, or better still, certain entire organs, very thin, transparent, and young, but fully formed, in which the latex has an abundance of globules, it is often easy to observe a translation of fluid, and to appreciate its rate of motion, by the time which the globules take in moving a certain space. In cases where the motion of cyclosis cannot be actually seen in the vessels, it may be inferred from the following fact. When the two ends of a stem containing milk are cut through, the latex is seen to run out at both ends of the fragment, which proves that there must be both an ascending and descending current: the same phenomenon is visible in plants having a colourless latex; therefore there must be a motion of ascent and descent in them also.

2. It occurs in the greater part of monocotyledonous and dicotyledonous plants, and the vessels in which it takes place, are so generally in connection with spiral vessels, that the presence or absence of the one is usually accompanied by that of the other. The situation of the vessels in which it is found is, in the root, stem, petiole, peduncle, flower, &c. The system of vessels, in the form of a delicate network, surrounds the cells, and even traverses their interior, in the most diverse directions. In the stems of monocotyledons, cyclosis occurs in the woody bundles, as also in those dicotyledons which have their wood in like manner separated into distinct cords. But, in the stems of dicotyledons where the wood is disposed concentrically, the vessels of the latex are either placed singly, in the parenchyma of the bark; or, which is most common, they either form a continuous envelope around the wood, or bundles arranged circularly, or

even scattered cords. Vessels of latex may even be found in the pith. Schultz finds them in communication with the curious glands which in Nepenthes line the pitcher, and secrete the water found therein. In the form of capillary vessels (vasa contracta), they are very commonly present in hairs, where they form a most delicate plexus. It is, however, difficult to prove that the streams visible in hairs are really ramifications of cinenchyma, and Meyen has even denied their existence, upon which M. Schultz says with some asperity: "Wonderful enongh, he has had them before his eyes, everywhere, in the fine anastomosing streams in which the sap circulates in the cells, without recognising them. These vessels pass through and round the different organs, particularly the cells of the secreting organs, like a fine spider's web, and are visible in many plants, for example in the species of Caladium and Arum, even after maceration."

3. The latex is a highly elaborated and highly organised juice, which is not formed immediately from the fluid nutrient matter absorbed from without. It is usually viscid, insoluble in water, often opake, coloured white, yellow, red, brown, and is also often transparent and colourless; differences that result from the nature of the organised globules it contains, which, according to M. Schultz, constitute the living part of the latex. These globules have an oscillating motion, and, like the globules of blood, they coagulate, and the liquid part becomes transparent. In many plants which, when old, have a milky latex, it is colourless when they are young; this depends upon the degree of concentration of the latex. Upon exposure to the air, latex separates into a coagulum of a tenacious elastic quality, and a serum, the former being sometimes analogous to caoutchouc. This property is not found in any other vegetable secretions. If we consider the organisation of the latex, the globules it contains, its property of coagulating and separating into serum and a sort of fibrine, we are tempted to believe that there exists a considerable analogy between it and the blood of animals. By these marks the latex may be known from ethereal oil, resin, gum, and other secretions sometimes found in the interior of parenchyma, and which are always trans

parent and destitute of globules.

Nevertheless, Link has unaccountably confounded with cinenchyma the turpentine vessels of Coniferæ. (Elementa, ed. 2., i. 196.)

4. The latex itself originates in the sap, which rises by the tissue of the wood, and introduces itself into the foliaceous organs, thence, after being elaborated, passing into the bark, where it is deposited in the vessels in its mature form. De la Baisse caused a Euphorbia to pump up water coloured red; the liquid ascended in the wood, reached the leaves, tinged the latex, and the colour spread from above downwards in the bark but M. Schultz only twice succeeded, after many attempts, at obtaining this result.

5. The function of the latex is to nourish the tissue among which it is found. Increase in the layers of wood and bark may be arrested, if by ligatures, or cutting off annular portions of the bark, the afflux of nutritious particles from above downwards is stopped. Now the latex is the only one of the fluids in the bark which can have a progressive motion, and it is therefore it which furnishes nutrition. Upon robbing Asclepias syriaca of a great quantity of its milk, it ceased to bear fruit, but it sustained no inconvenience upon merely losing its sap. In fact, the loss of only small quantities of latex injures plants very much. It is the phenomenon of autosyncrisis and autodiacrisis (attraction and repulsion of the globules) which produces assimilation and nutrition. In consequence of autodiacrisis, the molecules of latex escape through the sides of its vessels, to be conveyed to the parts requiring nutriment; while, on the contrary, autosyncrisis brings about the assimilation of the nutritious matter. In proof of which, it is found that the distribution of latex is most abundant in those parts where the greatest increase ought to take place, and that the rapidity of the cyclosis is greatest at the periods of developement, the temperature remaining the same.

6. The cause of the motion may be assigned to heat; for, when Acer platanoides was exposed to a temperature of -18° to 24° centig. (-2° to 11° Fahr.), the latex ceased to move, but the motion was re-established when it was brought into a warm room: to endosmose; for water will sometimes cause a

renewal of motion when it has stopped: to light; because that agent determines the direction of growth: to contraction, which is the effect of irritability; not however, a contraction with successive pulsations, as in arteries, but by a simultaneous action throughout the whole length of the vessel, whose latex is thus brought into a state of powerful tension. Contraction, however, cannot be the first cause of the motion, for it is not even sufficient to change the direction of the currents. When a vessel has been cut through at both ends, it has discharged all its contents by that end to which the current had been directed, and not by the other. But these are to be regarded as secondary causes only; the essential cause is the perpetual oscillation of the globules. They have an incessant tendency to unite and to separate, without the one tendency ever overcoming the other; and, as the organic (molecules) elements of vessels are of the same nature as the globules of latex, it follows that the walls of the vessels, and the globules they contain, have the same tendency to approach and retreat, as the globules themselves have with respect to each other. As this motion of coming and going takes place in a determinate direction, it necessitates and regulates the progressive motion of the latex. This law, says M. Schultz, is, for the physiologist, what attraction and repulsion are for the investigator of physical actions; it is final, and explains phenomena because it is itself placed beyond the reach of explanation. [This opinion is strongly objected to by the committee who reported upon M. Schultz's paper.]

7. Cyclosis is analogous to the motion of the blood in the lower animals, such as Nephelis vulgaris, Planarias, Nais proboscidea, and Diplozoon paradoxum; or in the fœtus of a fowl, before the heart is formed, when, as Malpighi and Wolff have shown, the blood moves spontaneously in the vascular apparatus. Nevertheless, although there is in plants no heart, or centre of circulation, it appears that there are certain foci, concerning which M. Schultz speaks thus (Comptes rendus, vi. 583.):- In Commelina cœlestis there is a bundle of laticiferous vessels, which are very delicate and filamentous, compact and united in the form of a net with