united with bases, forming either neutral or acid salts. By far the most widely distributed of the organic acids is malic; the bases are either organic or inorganic; the latter chiefly potassa and lime; the former comprise various nitrogenous compounds. The proportion of acids present varies greatly; it is dependent on external circumstances, but is usually greatest in the young growing parts, diminishing gradually with the age of the organ. In young organs they are most commonly present in the form of salts of potash, which is, at a later period, replaced by lime. In addition to their function in producing turgidity, these acids also play an important part in being the agents by means of which potash is absorbed through the root.

Metastasis and Transformation of Energy in Plants.*-A. Famintzin publishes an elaborate handbook on this subject, founded on the researches of Pfeffer, Detmer, and others. He classifies the subject under four heads, as follows:-(1) Chemical composition of plants; (2) Organic sources of nutriment; (3) Synthesis of organic compounds; and (4) The interchange of material between plants and their environment.

Under the first head the author includes not only the organic but also the inorganic constituents of plants; as also the crystalline deposits and cystoliths. The second treats of germination and nutrition, including that of insectivorous plants; and of parasites, whether containing chlorophyll or not. The theory of fermentation and structure of ferments is also included here; and the phenomena connected with fermentation are again discussed more in detail in the third part. The fourth section treats of the properties of naked protoplasm, the interchange of substance in a cell inclosed in a cellwall (diosmose), the absorptive powers of roots and leaves, the movements of gases and water, and the transport of protoplasmic substances. The author does not agree with Sachs's view that metastasis is always accompanied by a loss of weight.

Action of the different Rays of Light on the Elimination of Oxygen.+-J. Reinke has designed an apparatus for determining this much-disputed question, which he calls a spectrophore.

A horizontal bundle of rays passes from the heliostat through a vertical slit into the dark chamber, and then through a telescope objective at a convenient distance to a sufficiently large prism, placed at the least possible deviation from an angle of 60°, producing a sharp objective spectrum on a screen. The screen consists of two vertical level boards, which can be so moved in a slot that their edges can either be brought close together or placed at any distance from one another; any required portion of the spectrum being then allowed to pass through the opening. Immediately behind the screen is a large convex lens on which the rays fall, and are collected into a focus in a small image of from 1 to 2 sq. cm. By this means any required area of the spectrum can be cut off. When the screen is entirely opened,

* Famintzin, A., Metastasis and Transformation of Energy in Plants,' (Russian), 816 pp., St. Petersburg, 1883. See Bot. Centralbl., xvii. (1884) p. 97. + Bot. Ztg., xlii. (1884) pp. 1-10, 17-29, 33-46, 49-59 (1 pl.).

a white image of the sun is obtained in the focus; when the refrangible portion as far as the green is cut off, a red image; and in the same way a green or blue image can be obtained. In order to bring exactly equal areas of the spectrum under observation, a scale is placed exactly before the screen adapted to the dispersion of the prism, and prepared therefore to suit each particular prism; and the screen is then put in position. The prism was made sometimes of flint-glass, sometimes of bisulphide of carbon; and the action of the various rays of light was determined by measuring the number of bubbles of gas given off in a unit of time from a shoot of Elodea growing in water containing carbon dioxide.

The result of the experiments is depicted by Reinke in curves; the absolute maximum of evolution of gas was found to be unquestionably between Fraunhofer's lines B and C, and nearer to the former, corresponding to a wave-length of about 690-680. From this maximum the curve falls sharply towards the line A, somewhat less sharply towards E, and from these more gently towards H. If the absorption-spectrum of living leaves is compared with this curve, it is seen that the maximum of evolution of gas coincides with the absorption-maximum in the red, or with the absorptionband I, while no secondary maxima of evolution correspond to the secondary absorption-maxima II and III. The maximum of evolution of oxygen, and probably also that of decomposition of carbon dioxide, belongs therefore to those rays of the refrangible half of the spectrum which are the most strongly absorbed by chlorophyll.

From these facts Reinke draws the conclusion that the action of chlorophyll on the elimination of oxygen by plants is a chemical one; although the physical action of chlorophyll on which Pringsheim insists is not altogether excluded, since the strong absorption of the refrangible portion of the spectrum may be connected with this physical function.

Movements caused by Chemical Agents.-W. Pfeffer has observed that the motions of motile organisms and parts of plants are to a large extent brought about by the exciting action of special chemical substances, which, in very small quantities, exercise an attracting influence. The substance which exercises the most powerful influence in this way is malic acid, an acid very widely distributed through the vegetable kingdom. It is the presence of malic acid in the archegonium of ferns and Selaginellacea which attracts the antherozoids into the open channel; while the specific attracting substance for the antherozoids of mosses is cane sugar. The author was unable to detect the attracting substance in the cases of Marsilia, the Hepaticæ, and Chara. In the Schizomycetes there is no one specific attracting substance; but any good nutrient fluid has this power; they will move towards the substance which supplies them with most nutriment.

The proportion of malic acid in the fluid in which the antherozoids of ferns are swarming required to influence the direction of their * Ber. Deutsch. Bot. Gesell., i. (1883) pp. 524–33; also, Unters. aus d. Bot. Inst. Tübingen, i. (1884); 120 pp.

movements is very small, viz. from 0.01 to 0.1 per cent., in combination with any base (sodium malate was most commonly used); it is perceptible even when the proportion is so small as 0.001 per cent. Free malic acid has the same effect as an alkaline salt in very dilute solutions; but when more concentrated it has precisely the opposite effect, causing repulsion. A repulsion is effected by a mixture of 0.01 per cent. malic acid and 0.2 per cent. citric acid; or by 5 per cent. neutral sodium malate.

The presence of so small a quantity as 001 per cent. of cane sugar has a corresponding attractive force on the antherozoids of mosses. The specific attracting medium has not yet been ascertained which causes the collection of antherozoids around oospheres, as in the case of Fucus.

Bacterium Termo and Spirillum undula were powerfully attracted by a 1 per cent. solution of extract of meat or of asparagin; a higher degree of concentration repels the latter.

The author suggests that the familiar bending of organs in the case of carnivorous plants is due to similar causes.

Direct Observation of the Movement of Water in Plants.*G. Capus gives the following account of experiments on this subject, chiefly on the dahlia.

By means of a flat razor a tangential section is made in an internode, a few centimetres in length, cutting into the stem nearly to the depth of the vascular bundles; this cut must be slightly concave. On the opposite side of the stem, and at the same height, two notches are made penetrating to the pith, allowing this part of the stem to be raised so as to expose the medullary canal or pith. This is carefully taken out without cutting the primary wood at the bottom; a transparent section is thus obtained in which the vessels may be examined intact.

The Microscope is placed horizontally in front of the section prepared in this way on a cathetometer. The plant may be observed either growing in the open soil or in a pot. On the section is placed a drop of water flattened by a cover-glass fixed to the stem by a drop of Canada balsam, or held simply by capillarity. The section is then placed opposite the light, when the vessels and fibres of the wood are seen to be full of bubbles of air more or less numerous in strings. When the weather is damp, the sky cloudy, and the ground saturated, the plant contains more water, and there are but few bubbles of air. They are in greater numbers and larger when the weather is dry, and the plant directly exposed to the sun. As soon as the sun no longer shines on the plant, the bubbles of air diminish in size in the vessels and finally disappear, absorption from the roots exceeding transpiration. When, on the contrary, transpiration is relatively active, the index indicates the ascending movement of water in the vessels.

Rheotropism.t-This term is applied by B. Jönsson to the influence of running water on the direction of growing plants and parts

*Comptes Rendus, xcvii. (1883) pp. 1087-89.

† Ber. Deutsch. Bot. Gesell., i. (1883) pp. 512–21.

of plants. To this cause he attributes the motion of the plasmodia of the Myxomycetes. If a plasmcdium is placed on a piece or blotting-paper which dips into water at one end, it moves towards the source of water, attracted by the current of water caused by the capillarity of the blotting-paper. Plasmodia are therefore positively rheotropic. Spores of Phycomyces and Mucor sown on blotting-paper and fed by a current of a nutrient fluid, put out hyphae which grow with the stream, and which are therefore negatively rheotropic. Botrytis cinerea is, on the other hand, positively rheotropic. Roots of seedlings of maize and other cereals which hang down into a free current of water grow towards the stream; they are, like other roots, positively rheotropic.

Transpiration.-A. Leclerc has performed a series of experiments to determine the laws which regulate the amount of transpiration from the surface of leaves. In a perfectly saturated atmosphere he asserts that leaves do not transpire; they may even acquire a not inconsiderable increase in weight. If the figures obtained from experiments are represented in a system of rectangular co-ordinates, the curve of transpiration is found to correspond much more with the psychrometric than with the actinometric curve. The following are the general conclusions arrived at by the author:

1. Transpiration is independent of light. 2. It falls to zero in an absolutely moist atmosphere. 3. It is a function of the hygrometric condition of the air, and may be expressed with sufficient accuracy by the equation E = a(F-f)±c; where a is a coefficient varying for each plant, but invariable for plants in the same series of experiments; f the tension of the aqueous vapour existing at the time in the air; c a positive or negative constant. 4. When the transpiration of a plant is more active in the sun than in the shade, this depends (a) on the rays of heat, which always accompany the rays of light, and warm the tissues; and (b) on the activity of assimilation of the leaves in the light.

The yellowing of leaves is often due to the transpiration being checked. The disease of the vine known as "folletage," is due to the leaves withering and dying in consequence of excessive transpiration.

Transpiration-current in Woody Plants.†-J. Dufour continues the discussion on this subject, adducing fresh arguments in favour of Sachs's theory of imbibition; the currents also being assisted by filtration from cell to cell, especially through the agency of pitted vessels. Experiments are described carried on for the purpose of proving that the transpiration-current can only take place through the walls of the wood.

To these arguments R. Hartig replies, maintaining that the passage of water through the wood does not ordinarily take place

* Ann. Sci. Nat. (Bot.), xvi. (1883) pp. 231-79.

+ Dufour, J., Ueber den Transpirationsstrom in Holzpflanzen,' 1883. See Bot. Ztg., xli. (1883) p. 843.

Hartig, R., Die Gasdrucktheorie u. die Sachssche Imbibitions-theorie,' Berlin, 1883. See ibid., p. 844.

through the cell-walls, but by filtration from cell to cell; although the former may occur in special circumstances, as, for example, when all the fluid water has been removed from the wood by transpiration.

Origin and Morphology of Chlorophyll-corpuscles and Allied Bodies.-F. O. Bower gives a useful summary and discussion of the results of recent researches on this subject, especially those of Schimper, Meyer, and Schmitz which have already been noted here.

Under the heading of "the Trophoplasts" A. Meyer also gives † a summary of the results of the recent work on Chlorophyllcorpuscles.

Spectrum of Chlorophyll.‡-A. Tschirch continues his researches on "pure chlorophyll," the term which he applies to the product obtained by the reduction of chlorophyllan by means of powdered zinc. In the so-called "solid chlorophyll," obtained by evaporating pure chlorophyll in a glass vessel he notices a small displacement of the absorption-bands of the spectrum towards the red as compared with an alcoholic solution; and the same phenomenon is presented by chlorophyll dissolved and hardened in paraffin. In the solid chlorophyll of the leaf there is a much greater displacement in the same direction. This results, in the author's opinion, from the chlorophyllgrain being a mixture of two substances, pure chlorophyll and xanthophyll. A useful synonymy is appended of the terms employed by different writers in describing the various members of the chlorophyll group.

Portion of the Spectrum that decomposes Carbon Dioxide.§C. Timirjaseff maintains that a solution of chlorophyll is not, as held by Wiesner and others, decomposed most quickly by the yellow, but by the red rays. The decomposition of carbon dioxide, as well as the transformation of chlorophyll, is caused by one and the same group of rays absorbed by the pigment. The green group of rays is not absorbed at all by weak solutions of chlorophyll.

Chlorophyll in Cuscuta.-The parasitic Cuscuta have hitherto been described as entirely destitute of chlorophyll. F. Temne, however, finds distinct indications of its presence by C. europea. This was established by an evident green tinge, either of the whole protoplasm or of separate granules, especially in the inflorescence; by the spectrum of chlorophyll obtained in an alcoholic extract; and by direct evidence of the evolution of carbonic acid.

Work performed by Chlorophyll.1-From a series of experiments, C. Timirjaseff deduces the result that, where there is energetic decom

* Quart. Journ. Micr. Sci., xxiv. (1884) pp. 237–54 (1 pl.).

† Biol. Centrabl., iv. (1884) pp. 97-113.

Ber. Deutsch. Bot. Gesell., i. (1883) pp. 462-71 (1 pl.); and ibid., Generalvers, in Freiburg., xvii.-xxii.

§ Arbeit. St. Petersb. Naturf. Gesell., xiii. (1883) p. 10 (Russian). See Bot. Centralbl., xvii. (1884) p. 101.

Ber. Deutsch. Bot. Gesell., i. (1883) pp. 485-6.

Arbeit. St. Petersb. Naturf. Gesell., xiii. (1883) p. 9 (Russian). See Bot. Centralbl., xvii. (1884) p. 100.