and violet disc looks blue; a red and blue, purple. Considering the formation of the sensation of orange in this way the colour produced is indistinguishable by the eye from the same colour in the spectrum, but whilst the orange beam in the spectrum consists of rays of definite wave-lengths, and is not split up into further colours by passing through another spectroscope, the composite orange beam formed by the mixture of red and yellow rays, consists of rays of quite different wave-length (those corresponding to red and yellow), and is again split up into the original colours that formed it on traversing

the large one. When the colour is a bright and intense one, the white or black must be combined with it, that is, must be subtracted from the other three. The amount of the several colours used can be determined numerically by measuring the angle included in each coloured sector, and in this way Maxwell obtained his colour equations.

Maxwell's colour-box is an apparatus by which any two or three portions of the spectrum can be made to overlap, and the resulting light examined. This is by far the most accurate means of determining colour

mixtures.

a spectroscope. In fact it is only the sensation of orange, which is the same as the sensation of red and yellow combined; or, the mixture of red and yellow rays to form an orange sensation is a physiological and not a physical one. Hence we are led to conclude (in the words of Professor M. Foster), "That an orange ray awakens either a simple sensory impulse which developes into a complex sensation, or a complex impulse (formed of impulses corresponding to red and yellow) becoming converted into a mixed or complex sensation."

In this respect the eye differs strikingly from the ear; for two notes, when sounded together, do not give rise to an intermediate note. The ear is able to analyse such complex sounds more or less.

The facts gathered from the above experiments with the colour-top, are included in a more general statement in regard to colour mixture which Maxwell proved to be true; namely, that by combining white or black with any other three colours, which were sufficiently dissimilar, any other colour could be matched. To assist in the comparison a smaller disc of the colour to be matched is set on the face of

A

FLOSCULARIA ANNULATA.

LTHOUGH this floscule has not been described,

it was found (for the first time) in the summer of 1882, in a marsh pool on Tent's Muir, Fifeshire; but only two individuals were found at that time. I sent both of them to Dr. Hudson, of Clifton. One of them died on the long journey; the other survived, but, unfortunately, arrived in a sickly condition. It exhibited itself often enough, however, to enable Dr. Hudson to draw a very good sketch of it; but it was in so languishing a condition that it died before he could make a satisfactory diagnosis of it. In the summer of 1886, I found a few more specimens in the Black Loch, Perthshire, and this summer (1887) I have again fished a number of specimens out of the same loch; and these have afforded me ample opportunity for studying the creature's habits.

Its corona is a hemispherical cup, whose edge is cut into three lobes of unequal size, the lobe on the dorsal side being the largest. It differs from F. trilobata and F. Hoodii (whose coronæ also bear three lobes), not only in the form of the lobes, but in the

fact that the tips of the lobes only are crowned with short setæ (Fig. 4); whereas, with F. Hoodii and F. trilobata, there are double rows of setæ that run round the whole margin of their corona, a little below which are three bands or rings (Fig. 4 r) of a brown colour. The colour is due to granules floating in the fluid between the outer and inner membranes when viewed with transmitted light; but if examined as an opaque object, with reflected light, the colour of the rings is white. (Hence the reason it has been called F. annulata.)

At the bottom of the corona, just under the third ring, is the vestibule (Fig. 4 v), where is visible (in a good light) a contractile collar, with a horse-shoeshaped rim, clothed with vibratile cilia (Fig. 4 cc),

lips of the buccal orifice dart forward with a snap, and the prey is forced down, one by one, through the tube into the crop. The little victims may be observed wriggling about within the crop until they are caught by a pair of curved jaws which are situated at the bottom of the crop, and the entrance to the stomach (Fig. 4), which is called the maxillary process.

The action of the jaws is an upward motion, and at the same time they open out to seize the food and drag it into the stomach. It is indeed interesting to witness the operation. Sometimes the jaws close on the spherical body of a monad a little below its centre; and when it so happens that the jaws fail to clutch it, the spherical body rebounds back into the crop, just as a person grasping at an indiarubber

whose motion generates an inward current, which carries with it infusorians within the expanded mouthfunnel. When once a monad has entered into the vestibule corona, there is no escape, for if it please the palate of the floscule, its doom is sealed; for, although the creature will suffer at times one or two monads to swim about in its large mouth, yet at any attempt to pass out over the margin, the lobes are drawn together, and the passage is closed. At the bottom of the vestibule there is a slit with two lips, called the buccal orifice (Fig. 4 bo), to which is attached a tube that hangs into a chamber called the crop (Fig. 4 c), which moves with an undulating

motion.

When the floscule has got one or two monads within the vestibule, the collar contracts quickly, the

Fig. 5.-Floscularia annulata, ventral view.

ball with finger and thumb a little below its centre, produces the same result. This rebound shows the toughness and elasticity of the cuticula of these minute monads.

The jaws assist very little in the mastication of the food, as their function seems to be simply to drag it into the stomach. Digestion seems to be performed wholly in the stomach and alimentary canal, and these organs are lined with vigorous vibratile cilia whose operation serves to triturate the food. The ovary is an oblong sac with spherical transparent germs, but when an egg is well developed (Fig. 4 g) it is opaque and fills a large portion of the body cavity (Fig. 4 e), and when ready for expulsion the creature retires into its tube. The egg is at first forced half out of the vent, the animal then moves slowly out of

its tube and comes to an erect position with its corona fully expanded. It then remains in that way (if not disturbed) for nearly an hour, and then again retires into its tube to finish the operation of depositing the egg. With some apparent exertion the creature lays the egg well down into its transparent gelatinous tube close to its long foot. The foot itself (Fig. 4ƒ) is long and flexible, and is capable of great expansion and very swift contraction, for on the least alarm the creature retreats into its tube with lightning speed. A longitudinal muscle runs down the whole length of the foot and is strengthened by numerous fine muscular transverse rings from its junction with the trunk to its extremity, where there is attached a short non-contractile peduncle (Fig. 4 c) which terminates in a disk which is fastened to a leaf of sphagnum, or other aquatic plant, by a viscous fluid secreted by a gland at the extremity of the foot for the purpose. The respiratory or water vascular system in F. annulata is not easily traced, as its trunk is rendered rather opaque by whitish granules that float in the fluid between the outer and inner membranes. But when the creature is kept for two days in clear water without proper food, the creature is so starved that it becomes very transparent, so that the details of the internal organs can be traced with less difficulty. The slender tortuous vessels can be observed leading down to the contracting bladder, situated near the junction of the foot with the trunk (Fig. 4 c b). The F. annulata, like all the other species of the same genus, inhabits a transparent tube secreted by the animal itself, which not only serves to protect the creature itself from its natural enemies, but also serves as a protection for its eggs from the ravages of aquatic worms and larvæ, for although the material of the tube is tough enough to resist the attacks of a large number of worms and larvæ, yet there are some, especially of the larvae of the dragon-fly, with their powerful mandibles, which cut through the tube and devour both parent and eggs. The material of the tube is so transparent that the observation of its contents is comparatively easy.

The F. annulata deposits from three to six female eggs in its tube, which take about five to six days to hatch. Six or eight hours before the embryo bursts its shell, two red eye-spots are very conspicuous; also a ciliary motion, and a twitching of the whole contents of the egg, are observed. The twitching becomes yet more vigorous, until at last the embryo bursts through its shell and, propelled by a wreath of delicate frontal vibratile cilia, it soon finds its way out of its mother domicile, and swims rapidly round its parent; then strikes out with a graceful motion through the water, poking amongst the weeds in quest of a fitting place to start housekeeping on its

own account.

It seems to be rather particular in selecting a site to build its future residence. I have seen one alight on the leaves and axil of a plant in a dozen places,

before it made a final selection of a spot to fix its foot; and a few hours after the young floscule was encased in a thin gelatinous tube, with its foot, trunk, and corona (although smaller in size) developed in the same form as its parent.

I have not yet met with the male of F. annulata, nor even the male of the other three-lobed species. There are sixteen known species of the genus Floscularia; the males in eight of them only have yet been found, leaving the males of eight species to be discovered.

The males of those that have not yet been found are F. regalis, F. Mira, F. longicaudata, F. Algicola, F. trilobata, F. Hoodii, F. annulata, F. edentata.

The males of those species that have been discovered are F. coronetta, F. ornata, F. cornuta, F. cyclops, F. campanulata, F. ambigua, F. calva, F. mutabilis.

The whole sixteen species of the genus Floscularia are inhabitants of fresh water, with the single exception of F. ornata, which is now known to inhabit both fresh and salt water. I had the good fortune to find the F. ornata very plentiful in tide pools at the mouth of the Firth of Tay in the summers of 1885 and 1886.

The length of full-grown specimens of F. annulata is from to of an inch.

Dundee.

JOIN HOOD, F.R.M.S.

FURTHER NOTES ON THE TOOTHWORT (LATHRÆA SQUAMARIA).

EACH year, since 1883, when I first found L.

squamaria in the locality indicated by G. E. Smith, in his "Plants of South Kent," published in 1829, I have visited the place, and on each occasion have found the plants all bearing the characters I described in SCIENCE-GOSSIP, January, 1884. In connection with my notes of that date, I would remark that it has been thought that Smith's plant was an old one, gone to seed, and that mine was a young, imperfectly developed plant. The editor's note, page 143, vol. xx. was in reference to specimens I sent him in full seed, and which were quite as crowded as the plant photographed by me. I have not yet found any plant in the least approaching that described and figured by Smith.

The plants I gathered in 1883 were growing in a section of the copse, which I will call for reference No. 1, and which had remained undisturbed for, I should say, from fifteen to eighteen years. There was but little undergrowth; the hazels, &c., being well up. In an adjoining section of the same copse (No. 2) of about two years' growth, I, together with several others, searched most assiduously for the plant, but without success. During the winter of that year, No. I section was cut down, and in 1884 there were

comparatively few specimens to be found, and none in No. 2 section. In 1885, I found but three specimens in No. I section, and again none in No. 2.

In 1886, I could not find a single plant in No. I section, although I paid several visits, and took with me several good searchers; but in No. 2 section I found two plants.

In 1887 I was still unable to find any plants in No. 1, while in No. 2, which is now about six years old, I found the plant in comparative abundance. Of course, during the first few years following the cutting down of a copse, the undergrowth is very considerable, and the difficulties of finding so small a plant as L. squamaria are great. But I feel convinced, from my experience, that its appearance is influenced (like that of some other woodland plants) by the condition of the copse with regard to its undergrowth.

That it has a most remarkable vitality, the following (communicated to me by G. B. Wollaston, Esq., of Chislehurst) will show. He informs me that he had a plant of L. squamaria in a flower-pot for about twenty years, during which time it never appeared above ground, but that at the end of the twenty years it was as sound and fresh as when first put into the pot. Its not appearing above ground was of course due to its want of food supply, it being parasitic.

Plants that have acquired the habit of parasitismwhether partial or complete-may naturally be expected to afford evidences of the time when they lived free and independent lives, in the retention or partial retention of organs or peculiarities of structure, which were absolutely necessary for them in their free and independent condition, but which are now of no further service to them, the host performing the function for the plant which its own structure enabled it then to perform for itself.

The animal world affords numberless instances of useless and aborted organs, evidently remnants of a previous condition of existence requiring a different organization; and in the vegetable world, no doubt, the instances will be found as numerous when the same amount of attention has been given to it. We already know of many modified leaves, aborted and imperfectly developed styles, &c. &c., and as our knowledge of the physiology of plant-life increases, it may reasonably be assumed that many remnants of a past condition will be discovered. That they will be so marked and diverse as in the animal world we should not expect; the functions and surroundings of the one being so many and various in comparison with those of the other.

plant for their original function, and of the modification of those organs, adapting them to the performance of a new and totally different one. If a transverse section be made of one of these scales, it will be found to possess several irregularly-shaped cavities (Fig. 6), and on the walls of these cavities will be found numerous little gland-like bodies.

These little bodies have been noticed by many observers; but what special function they perform has not (so far as I can learn) been hitherto discovered. In addition to these gland-like bodies, and scattered between them on the surface of the cavities will be seen numerous symmetrically arranged cells, reminding one of stomata. What function, however, could stomata possibly perform in this enclosed cavity? Certainly not the ordinary function of respiration. But that they are stomata, although perhaps useless and aborted, I think I have sufficient evidence to prove. Also that the little gland-like bodies are really glandular hairs, which, together with the stomata, occupied their usual position on the inferior side of the leaf of the plant before it acquired its parasitic habit.

How, why, and when L. squamaria took upon itself the habit of parasitism, are questions that can be answered by speculation only. That the habit was acquired gradually, we infer from observation-since changes in habit, and still more in structure, can take place but slowly.

Probably the first act towards parasitism was the developing of cells, which, coming into contact with some other growing vegetable substance, had the power of attaching themselves to it; and as L. squamaria is a succulent, rapidly-growing plant, it helped itself to the nutriment of its neighbour through these attached cells. This habit gradually grew until the plant became, as we now find it, wholly dependent for its existence on some strong and vigorous host.

Probably this proclivity to parasitism was brought about by the circumstances of its environment. What these were we cannot know; but that the habit became necessary to its existence we may be sure, and also that the cells possessing the function of attachment and absorption must be considered as a development or adaptation for this special function. As the habit of parasitism developed, the leaves and roots would gradually give up their own special functions, and, if suitably positioned, would adapt themselves to the new order of things; the plant either losing them entirely or partially, or modifying them to new functions. Thus the leaves of L. squamaria appear to have become modified.

An examination of the very young scales will reveal the fact, that they have apparently started life as ordinary leaves; instead, however, of developing a flat blade, as in an ordinary leaf, the young leaf takes a sharp bend downwards, and folds back upon itself, as in Fig. 7. The cells of the leaf

which come into contact, due to this folding back, are apparently possessed of the power of uniting, and thus forming the cavities seen in a longitudinal section. The formation of these cavities is due to the linear growth of the aborted leaf; the bending back of the leaf first takes place, as just remarked, when very young and small. Points, probably of the raised ribs near the apex, are brought into contact with other points near the base; attachment takes place, thus forming the first cavity; the leaf, by growth, increases in length, both between the points of attachment and the apex, and the same points and the base, which, after proceeding a certain distance, again come into contact and unite, forming a second cavity, and so on (Fig. 7). A transverse section reveals cavities that radiate from the stem. These are probably caused by the uniting of the underneath ribs of the leaf; for through each partition wall, between the cavities, may be traced the vascular bundles which ran through the ribs of the leaf in its earlier history, and which are continued through the base of the leaf into the stem, as seen in the transverse and longitudinal sections (Figs. 6 and 9).

The cavities in the scale are sometimes separate and distinct from each other, but more generally several, or even all, are united, forming one large cavity with deep recesses.

The apex of the leaf or scale, folded back upon the base, is never attached cell to cell, the tissue here never being continuous. It is, however, invariably pressed quite close; so close indeed, that in the cavity of a fully-developed scale I have never found any extraneous matter (I shall, however, refer to a younger scale later on). Fig. 9 is a fair example of the numerous scales I have examined. Hence, though these cavities are not hermetically sealed by cell-fusion, they may be considered practically airtight, and may thus be correctly termed enclosed cavities, and, as such, they will render the stomata useless. It must not, however, be forgotten that the united cavities converge to the apex, which suggests that some time in the past they were in communication through an opening here, with the outer air; and also the probability of the stomata carrying on their function in a gradually lessening degree, until the opening was finally closed.

With regard to the method of development of the scales, I am at a loss to determine whether it is due to a folding back, and attachment taking place as described, or whether, after the folding back, caused by the cells of the ribs not being developed at the same speed as those of the lamina, has taken place, these former are (subsequently) developed with a speed equal to the growth of the lamina cells, and continuity is thus preserved. This appears to me to be a question presenting great difficulties, as it is highly probable that both methods obtain; the first in order being the method by attachment, gradually

superseded by the continuous method, which latter may be replaced in course of time, if needed, by the production of the thick fleshy scale, without any break in the continuity of its tissue from the stem.

From these observations it will be seen that, whichever way the development of the scales may take place, it is such that the stomata and glandular hairs of a previous condition are enclosed in cavities, which may, in the course of development, altogether disappear, cell tissue taking their place.

If it be true, that the leaves of L. squamaria have become aborted as leaves, and developed into

thick fleshy scales, it then follows that these scales must have a definite function to perform, for it does not appear feasible that such large and numerous appendages should be retained and developed without serving some purpose in the economy of the plant. The primary function of these scales I believe to be one of food-storage; the attachments of the plant to its host, as we shall presently see, while perhaps numerous, and in some cases very complete, do not seem sufficient to maintain the rapid growth of the thick succulent stem, the comparatively large flowers, and the production of the numerous seeds. The