Since my communication in the last number of this Journal, “On the Circulation of the Sap in the Leaf-cells of the Anackaris Ahinastrum” I have continued some investigations on non-aquatic plants, with the view of ascertaining the relation or analogy, that the phenomena of their circulatory movements display, towards the subject of my former paper, and to each other respectively.

I must, however, remark in the first place, that the examples have been examined in a very random manner, for I take up the microscope at uncertain periods, merely as a means of recreation, and make no pretensions to that order and system, which alone would allow the efforts of my pen, to find a place with those of a scientific and professed botanist. I am merely desirous of recording some facts which I believe have not before been noticed.

The movements of circulation are best seen in the hairs of plants, as the transparency and uniformity of their substance allows their internal mechanism to be very readily distinguished. I had commenced a list of the most remarkable, and after extending the catalogue to upwards of one hundred, I concluded that the difficulty was to find the exceptions, for hairs taken alike from the loftiest Elm of the forest, down to the humblest weed that we trample beneath our feet, plainly exhibit their circulation. Even hairs from the upper surface of a blade of common Couch Grass (Agropyrum repens) display the sap-movement with singular beauty and distinctness, considering the minuteness of the object; (the intermediate diameter being less than 1-1000th of an inch). The particles may be seen traversing straight from the base towards the apex of the hair, and returning again 5y the opposite side.

The circulation in the hairs of the Groundsel (Senecio vulgaris) was first announced by Mr. Holland, as a discovery made by his triplet microscope, and it is a remarkable instance of what his instrument was capable of performing, for out of the multitude of vegetable hairs in which the sap-motion can be seen, I consider this to be one of the most difficult; for with our best compound microscopes, it requires careful management, and a trial of several fresh specimens before it can be shown satisfactorily.

Hairs that exhibit circulation may be taken from all parts of the plant, as the leaves, flowers, stalks, and fruit, and even from the ripening seed-pods as in the Snap-dragon (Antirrhimum) and White Mustard (Sinapis alba), &c. It is important that the specimens should be gathered from a portion of the plant, in a healthy and vigorous state of growth. The time is also of some consequence, the motion of the sap being generally most rapid about mid-day. The specimen must be examined as soon as possible, and the hairs detached without touching them, by tearing them off with a portion of the cuticle of the plant to which they are attached, by means of a fine-pointed forceps. If the hair itself is grasped the destruction of its vitality is the usual consequence. The object should be instantly placed in a thin glass compressor with clean water, using a good eighth object-glass and an achromatic condenser having a series of diaphragms. Daylight is infinitely superior to artificial illumination, and I have found it much preferable to use a right-angled prism instead of the ordinary plane mirror.

In cold dull weather, a well-known object will sometimes fail to exhibit its circulatory movements ; in such a case, it may be called into activity by means of the natural stimulus of heat. In applying this the object need not be removed from the microscope, as a stream of hot air may be blown on to the upper or under surface of the thin covering glass, until the sap current is seen to move, by means of a metal blowpipe, or the stem of a tobacco-pipe, previously heated in the flame of a spirit-lamp. Some plants always require the application of an increased temperature, in order to show their circulatory movements. The hairs of the Helianthus are a good example of this.

In the hairs of the numerous variety of plants that display the sap-circulation, each species exhibits somewhat different and peculiar features, which may be considered, in a degree, characteristic throughout the plant; in some, single lines of sap-currents extend the entire length of the cells or hairs, and in others they are divided into an irregular network of ramifications, which shift their positions with considerable celerity, the diversity of the phenomenon, perhaps, depending in some measure, upon the constitution and fluidity of the sap, for where this is rather glutinous the current traverses in the form of a sluggish uniformly moving sheet or layer, lining large portions of the interior of the cell; I may mention hairs from the Elder (Sambucus niger) as an instance of this.

In all cases where the sap-motion is seen in the hairs of a plant, the leaf-cell displays analogous peculiarities, provided the cuticle is not too opaque, or strongly marked to obstruct vision. The cells are best obtained, by tearing off- a layer of the cuticle from the stalk or midrib of the leaf, and must then be examined as speedily as possible, for the specimen loses its vitality much sooner than the hairs. There is scarcely a portion of a leaf-cuticle possessing the requisite transparency, taken from any plant wherein I have not discovered indications of circulation; even where there is no direct motion of particles to be seen, on account of their minuteness, the existence of circulation may still be known, from the following fact:—The active corpuscles, which are the primary cause of all the circulatory movements, are remarkable for their high refractive power, both on their completion, and in different stages of formation, and when arranged in a moving train, they appear as bright lines across the cell. *

Many specimens of leaf-cuticle, in which at first no movements whatever can be discovered, exhibit these lines, which on being carefully watched, are seen to alter their relative positions, a condition evidently depending upon progressive motion. Most leaf-cells, of course, contain chlorophyll-granules ; I have occasionally seen a few of these kept in a continual motion by the sap-currents, but never in any instance with the same degree of vigour and constancy, as in aquatic plants. In the cells of the common Plantain (Plan- tago’) a few chlorophyll-granules are sometimes seen in motion. This plant furnishes an excellent object, as the cuticle from the stalk or midrib of the leaf shows circulation, both in the hairs and cells at the same time; the sap-motions round the latter are occasionally quite as plainly seen as in the Anacharis, but more frequently the current is one of extreme tenuity, and travels round the cell-wall with great velocity.

In the cells of the Horse Thistle(Cnicus) I have also seen the chlorophyll-granules carried along with considerable vigour by the sap-currents : this plant exhibits a remarkable variety in the phenomena of circulation. The glutinous corpuscles are connected together in the form of a line, or rope stretched across the cell, exhibiting a loose vibratory motion as if it were being shaken at one end, while particles and, occasionally, chlorophyll-granules, are carried forward in a manner resembling beads along a string.

Having now noticed some of the distinguishing peculiarities of the circulation in a few of the plants that have come under ray observation, I will offer some brief remarks on the vital principle of vegetable growth and motion. I had stated in my former paper that the cell-circulation, or what is termed “rotation,” in the Anacharis, is entirely caused by the combined effort of a multitude of active corpuscles; the same fact equally applies to every other plant that I have examined ; and subsequent experience has given me some further insight into the nature of these atoms ; they evidently derive their origin and formation from the most fluid portion of the sap, with which every cell is filled, and which pervades all other portions of the plant tissues. In every stage of their growth they individually possess the motion peculiar to active molecules, but when in combination in their containing cell, this motion is converted into one of direct progression from some cause that I am not able to explain. I have tried by various means to effect a similar motion artificially in ducts and tubes, with both organic and inorganic active molecules, but without success ; I therefore conclude, that the progressive movement is not due to any mechanical conversion of one force into another, but arises from some unknown property, connected with the vitality of the plant. I have witnessed the effect in numberless instances in both the cells and hairs of plants. An isolated active corpuscle is seen detached, quickly performing its vibrations with constant activity, until its progress becomes arrested by one of the various ramified currents which traverse the hair; at which instant the vibratory movements totally cease, and the particle visibly assists the direct-forward motion of the current by its vital energy.

I observed with regard to the Anacharis, that after having been kept in a cold, dark place for one or two days, usually not a symptom of circulation could be discovered, the corpuscles having collected together in heaps, with the component particles in a state of torpidity, and on being again exposed to the stimulus of light and heat, they recommenced their active motions. This effect is still more remarkable in some non-aquatic plants; and a practised eye may at once detect, by the state of the cell-contents, whether the plant is in a state of repose or hybernation, as the corpuscles will in this case be seen collected together in several gelatinous-looking clots, their dormant vitality being again called into existence, by the same method as described for the Anacharis. Light is also quite as necessary a stimulus as heat; for in a recent experiment on this plant I interposed four thicknesses of blue glass between the achromatic condenser, and luminous source, (bright skylight,) thus entirely intercepting the heating rays, and yet, in spite of this intervening obstacle, speedily succeeded in exciting the movements of circulation.

The microscope discovers that in every portion of the plant each duct, cell, or vesicle, that is filled with sap, also contains active corpuscles, apparently differing in dimensions and substance according to locality. As regards the office that these bodies fulfil, it may be inferred that either they are the vehicles that convey nourishment to different portions of the cell-tissues, or that they themselves are deposited, to form the various structures of the plant. I will give an illustration of the latter effect. The annexed woodcut represents one of the hairs or spines taken from the stalk of the Anchusa paniculata (Boraginaceœ), an ornamental flowering plant of rapid growth. The growth of the spine is performed by the addition of successive layers to the interior, as shown at a, a, which eventually fill up the apex and render it solid : the method by which this action takes place is as follows:—A dense current of corpuscles are seen to travel along one wall of the spine, constantly returning by the opposite side, represented at b b. At c, where the deposition occurs, there is a considerable accumulation, and at the boundary, where they are converted into the substance of the spine, a number are seen to be adherent. Some are but recently deposited, while the underlying ones are in various regular stages of transition, gradually losing their form and outline, and finally all traces of individuality become lost; and by a species of induration the particles become united and identified, with the solid body of the spine.

In very many specimens of this object that I have submitted to examination, the deposit has been so rapid, that there was not sufficient time for the complete condensation of the component corpuscles. In these instances a number of them have been caught and loosely enclosed in one or more cavities, as shown at d d, and, with the exception of being perfectly motionless, the contained corpuscles are the exact counterpart of those circulating in the spine. The walls of the containing cavities do not possess a definite outline, because they are lined with corpuscles in all their transition stages.

I have now brought forward the chief substance of my notes on this subject ; they were made without previous study, and with an intention to avoid all hypothesis, and to confine myself to as clear a description as I could give, of any facts that the microscope might reveal.

There is yet very much to be learned respecting the sap-circulation of plants, particularly in their different organs ; but the inquiry is attended with much difficulty, from the necessity of our being compelled to examine detached and lacerated specimens. In many examples this is not of material consequence, as in some aquatic plants, for in these the cells retain their independent motions and individuality, long after their separation ; but in nonaquatic plants the case is somewhat different, for the mutual dependence of neighbouring cells is so considerable, that in many instances, death is the immediate result of detaching them, and the movements immediately to be seen under the microscope, are probably only the lingering remnants of vitality, and do not perfectly represent the circulation in the uninjured plant.

Lest it should be imagined, that I advocate the long-exploded theory, that supposed all vitality to originate with active molecules, I will venture, in conclusion, to make a few brief remarks in relation to them. The existence of active molecules has been known in a very early age of the microscope, but the first definite information on the subject, was given in the paper of Dr. Robert Brown, published in the ‘Edinburgh Journal of Science,’ for July, 1828. These observations rather tended to favour the above theory than otherwise, from the circumstance of his connecting together, without due distinction, both inorganic and organic molecules, some of the latter being obtained from actual living plants. The difference between vital and inorganic molecules is immediately perceptible, when submitted to the action of proper tests. Active molecules may be obtained from very many different mineral and inorganic bodies, as sulphur, limestonerock, ashes, and even burnt clay. Their motions have been successively attributed to the influence of mutual attraction, caloric, and electricity ; I have tried several experiments upon them with these two agents, but without obtaining definite results ; nor am I yet satisfied with any explanation that has hitherto been given of the cause of their activity. I merely mention this in order to show the very wide difference existing between these and the active molecules, or rather corpuscles, contained in the vegetable cell; to all appearance their movements are identical, but the motion of the latter may be entirely suspended, or awakened, by the range of temperature consequent upon ordinary atmospheric changes. Their vital activity is immediately destroyed by a small trace of hydrochloric or sulphuric acid. The motion is increased by the agency of a slightly-alkaline solution, particularly that of ammonia; but this stimulant added to excess becomes a poison, and destroys the principle of activity. *

On the other hand, active molecules obtained from a powdered brick-bat, for example, may be exposed to considerable differences of temperature, without their motions being affected by it; and provided there is no chemical decomposition, they exhibit the same degree of energy, whether the solution be either acid or alkaline

*

As these observations were intended to be exclusively confined to thesap-circulation, I have been desirous of recording them in the simplestmanner possible, and have therefore avoided technical expressions ; whatI have termed “the investment of active corpuscles,” has been knownas “protoplasm,” or “cell-mucus.” It may be doubted whether theseterms are strictly applicable, or truly represent that which in realityconsists of a multitude of particles, possessing individual activity anddiffering in size, and probably in chemical constitution, according to localposition and the variety of plant-substance and tissue with which theyare ultimately destined to combine, such as cellulose, and the loose contentsof the cell, as chlorophyll- and staich-granules, the latter being mostevidently formed by the successive deposit of external layers upon acentral nucleus.

I may also remark, that it was formerly supposed, and some even nowretain the same opinion, that the “circulation,” “rotation,“” gyration,“or” cyclosis, “in the vegetable cell, both in its early development, orgrowing stages, was in some way connected with a central nucleus, alsokept in rotation, and termed the” cytoblast.” I consider this suppositionto be entirely fabulous, for whenever I have occasionally observed such anucleus, it has either been formed by an accidental conglomeration of someof the cell contents, or by morbid conditions.

*

A fact curiously in accord with what has been observed by Ktilliker,with respect to the action of the jsame re-agents upon the spermatic filamentsof animals.—Vide’ Quarterly Journal of Microscopical Science,’vol. iii., p. 293.—[EDS.]