substance of this description imbedded in a brown cell-sap, Enothera biennis, Cerinthe aspera, Calendula officinalis, Tagetes glandulifera, Viola tricolor, Rudbeckia laciniata, Digitalis ambigua, and Salpiglossis variabilis. The particles of the pigment are often in a state of active molecular movement; they are always coloured green by iodine, and are soluble in concentrated sulphuric acid with a deep blue colour. In some other chemical reactions they vary. The pigment appears to be always imbedded in a matrix of protoplasm. A solid red pigment was observed in the fruits of Rosa canina, Pyrus aucuparia and Hostii, Convallaria majalis, Bryonia dioica, and in the aril of Euonymus latifolius and europæus, Celastrus candens and Taxus baccata. The red pigment in the cortical portion of the root of the carrot is of a very peculiar kind, resembling long pointed crystals. The cells of the scarlet berry of Arum maculatum contain a great quantity of minute brownish-red granules. Insoluble violet pigments are rare, but occur in Thunbergia alata and Delphinium bicolor; while blue granules are found in the fruit of Viburnum Tinus. Brown insoluble pigments were found only in seaweeds, Fucus vesiculosus and Furcellaria fastigiata. The development of the coloured granules does not end with their acting as pigments; after this period they go through a variety of changes of development or degradation. Movement of Sap in Plants in the Tropics. *-Observations made in Europe show that the activity of the circulation of the sap has two periods of maximum in the 24 hours, one in the morning, the other, less pronounced, in the afternoon. V. Marcano has carried on a series of experiments to determine whether the same is the case in the tropics. They were made at Caracas in Venezuela, about 101° N. lat., at a height of 869 metres above the sea-level, where the barometric pressure scarcely varies from 1 to 2 mm., and the thermometer not more than 3° in the 24 hours. The plants observed were Carica Papaya and liane. By means of a manometer, two very well marked maxima in the rapidity of the movement of the sap were detected, the first between 8 and 10 15 A.M., after which the curve rapidly sinks to zero, remains there for a time, and then rises, between 1 and 3 P.M., to a much smaller height than in the morning, sinking then again gradually to zero, the activity commencing again after sunrise. Exudation from Flowers in Relation to Honey-dew.†-T. Meehan refers to the fact that standard literature continues to teach that the sweet varnish-like covering often found over every leaf on large trees, as well as on comparatively small bushes, was the work of insects, notably Aphidæ. Dr. Hoffman, of Giessen, who in 1876 published a paper on the subject, is the only scientific man of note who takes ground against this view. He met with a camellia, without blossoms, and wholly free from insects, and yet the leaves were coated with "honey-dew." He found this substance to consist of a sticky colour * Comptes Rendus, xcvii. (1883) p. 340. less liquid, having a sweetish taste, and principally gum, and Mr. Meehan has often met with cases where no insects could be found, as well as others where insects were numerous, and where in the latter case, the attending circumstances were strongly in favour of the conclusion that the liquid covering was the work of insects. He considers that few scientific men have any knowledge of the enormous amount of liquid exuded by flowers at the time of opening, and he has seen cases where the leaves were as completely covered by the liquid from the flowers, as if it had exuded from the leaves, as he considers Dr. Hoffman had good grounds for believing is often the case. What is the object of this abundant exudation of sweet liquid and liquid of other character from leaves and flowers? We are so accustomed to read of nectar and nectaries in connection with the crossfertilization of flowers, that there might seem to be no room for any other suggestion. But plants like Thuja and Abies are anemophilous, and, having their pollen carried freely by the wind, have no need for these extraordinary exudations, from any point of view connected with the visits of insects to flowers. In the case of Thuja, Sachs has suggested another use: "The pollen-grains which happen to fall on the opening of the micropyle of the ovules are retained by an exuding drop of fluid, which about this time fills the canal of the micropyle, but afterwards dries up, and thus draws the captured pollen-grains to the nucellus, where they immediately emit their pollen-tubes into its spongy tissue. In the Cupressineæ, Taxineæ, and Podocarper, this contrivance is sufficient, since the micropyles project outwardly; in the Abietineæ, where they are more concealed among the scales and bracts, these themselves form, at the time of pollination, canals and channels for this purpose, through which the pollen-grains arrive at the micropyles filled with fluid." ”米 In his former observations on liquid exudation in Thuja and other plants, Mr. Meehan was inclined to adopt the suggestion of Sachs as to the purpose of the liquid supply; but as it was present in Abies so long after fertilization must have taken place, and as it was held up in the deep recesses of the scales of the pendent cone, where it could hardly be possible the wind could draw up the pollen, we must look for other reasons, which, however, do not yet seem to be apparent. Latex of the Euphorbiacea.†-S. Dietz has studied the composition of the latex of various plants, especially of the Euphorbiacea. He finds almost invariably crystalline substances to be present which crystallize out when the latex is made to coagulate under the coverglass. In the Euphorbiaceae he distinguishes three kinds of crystallizable substances, as follows: 1. Sphærocrystals. These differ in their mode of development from any hitherto known. In the coagulated latex of the Euphorbiacea *Sachs' Text-book of Botany,' 2nd Engl. ed., 1882, p. 513. M. Tud. Akad. Ertek., xii. (1882) 23 pp. (2 pls.). See Bot. Centralbl., xvi. (1883) p. 132. there arise separate dense spherical groups, becoming gradually denser as the solvent evaporates, in consequence of which, when crystallization commences, an empty space is formed in the interior of the sphærocrystal. The sphærocrystals of the Euphorbiaceae are organic in their nature, and all belong to the inulin type. They occur in especially large numbers in the coagulated latex of Euphorbia splendens, heptagona, and erosa, in the last species with a diameter of 0.8-1.0 mm.; also, less developed, in axial organs of the two firstnamed species. The latter differ from other sphærocrystals in dissolving in glycerine after from four to eight weeks' immersion. 2. Resin-crystals were found in the latex of all species of Euphorbiaceae examined, belonging to the cubical system. They are of three kinds :-viz. (1) forming angular dendritic groups; (2) groups consisting evidently of closely packed separate crystals; (3) those which occur only isolated. 3. Crystals consisting especially of potassium and calcium malate. These belong mostly to the rhombic and to the bi- and uniaxial systems. True crystals of salts of malic acid also occur, to which he gives the name of stellate crystals. Crystalloids in Trophoplasts, and Chromoplasts of Angiosperms.*-Pursuing his previous investigations of starch-generators or trophoplasts,† A. Meyer has come to the conclusion that the bodies described by Schmitz in algae under the name of pyrenoids are identical with the crystalloids of proteinaceous substances which frequently occur in the fusiform trophoplasts of many flowering plants. They differ from the protoplasm in having no framework or plastin. The crystalloids of Phajus swell and dissolve with greater or less readiness in water; they are completely soluble in solution of chloral hydrate; when hardened by alcohol they are soluble in cold potashlye, but not when hardened by mercuric-chloride; they are colourless, homogeneous, and doubly refractive; when hardened by picric acid they are distinctly stained red by alum-carmine, but less easily than the nucleus. In most of these characters they agree altogether with Schmitz's pyrenoids. The autoplasts of foliage-leaves are usually formed as follows:The comparatively small trophoplast of a meristem-cell, which is at first colourless and globular, or more or less regularly stretched by the surrounding protoplasm, begins to grow slowly with the protoplasm of its mother-cell. The framework or plastin thus increases in mass, and grains of chlorophyll are formed within it, and possibly other at present unknown substances soluble in alcohol. The mature autoplast appears to have changed its structure before it exhibits any change in colour. The trophoplasts of the petals of angiosperms are usually smaller than those of the foliage-leaves, but do not differ from them in any essential respect. The trophoplasts of foliage-leaves may be classed under the four following types: -(1) colourless *Bot. Ztg., xli. (1883) pp. 489-98, 505-14, 526-31. Ibid., iii. (1883) p. 405. during the whole of their existence; (2) at first colourless, then forming chlorophyll, which remains till the death of the cell; (3) colourless and forming chlorophyll, which afterwards passes over into xanthophyll; (4) colourless, producing xanthophyll directly sooner or later; (5) coloured by xanthophyll during the whole of their existence. The chromoplasts of flowers may be classified as follows:-A. In the last stage of development round, or (in the epidermis) more or less angular from mutual pressure, never fusiform. (a) They produce comparatively little xanthophyll, and appear at last more or less flat and irregularly filled with vacuoles; xanthophyll light yellow. (b) They produce comparatively little xanthophyll, and contain till the end a great quantity of starch; xanthophyll light yellow. (c) They produce a comparatively large quantity of xanthophyll, and are finally more spherical: a. with none or very few vacuoles, and xanthophyll reddish yellow; B. xanthophyll light yellow. (d) They produce a comparatively large quantity of xanthophyll, which finally lies within the protoplasm in a granular form. B. They finally become fusiform from the tendency of the xanthophyll to crystallize; xanthophyll usually dark or reddish yellow. C. They produce crystalloids in or on them, by which they are more or less stretched. Of each of these types, between which there are transitional forms, the author cites examples. Formation and Resorption of Cystoliths.*-According to J. Chareyre, the reserve-materials of the Urticines and Acanthacea consist of aleurone-grains, each of which contains a globoid; Acanthus and Hexacentris also contain starch. The globoids which constitute the calcareous reserve-materials of the seed disappear more completely if the plant is cultivated in pure sand than in limestone or ordinary soil; but they do not contribute to the formation of cystoliths. In pure silica the pedicel only of the cystoliths is formed. In darkness only rudimentary cystoliths are produced. In the Acanthaceae etiolation and death produce no effect on the cystoliths; but in Ficus elastica the calcium disappears in darkness after about fourteen days. The resorption of the calcium carbonate does not result from its passing over into the alkaline carbonate. Under normal conditions, the cystoliths are formed again in a month or six weeks. Calcium oxalate behaves in the same way. In etiolated leaves of Ficus, sulphuric acid produces a larger quantity of crystals of gypsum than in normal leaves. Function of Organic Acids in Plants.†-W. Detmer regards the organic acids as having a very important function as the chief promoters of osmose, and consequently of the turgidity of the cell. The conversion of starch into sugar is also greatly dependent on the presence or absence of free acids; the presence of carbonic acid and of small quantities of hydrochloric, nitric, phosphoric, citric, and oxalic p. 389. *Comptes Rendus, xcvi. (1883) pp. 1594-6. Cf. this Journal, iii. (1883) + SB. Jenaisch. Gesell. Med. u. Naturw., 1883, pp. 47-9. acids promoting this conversion by means of starch in a remarkable manner. Absence of these acids not only decreases the transformation of starch but also the turgidity of the cells; but this conversion can only be effected by the combined action of the acid and of the ferment. Formation of Ferments in the Cells of Higher Plants.*- A series of experiments by W. Detmer leads him to the conclusion that in the cells of higher plants no transforming ferment can be produced in the absence of oxygen. Access of free oxygen is an essential condition for the formation of diastase, and the ferment is unquestionably formed by means of oxygen out of the albuminoids or proteids of the protoplasm. Poulsen's Botanical Micro-Chemistry.t-This book, after having been translated from the original Danish into German, French, and Italian, at last appears in English, having been translated, with the assistance of the author, and considerably enlarged by Professor W. Trelease, of Wisconsin, U.S.A. We referred to the original work (i. 1881, p. 772) but we may quote the following paragraphs from the introduction as showing its Scope: Physics has thus striven to bring the Microscope to as great a degree of perfection as possible; it remains for chemistry to find means of recognizing and rightly understanding the composition of the objects we investigato. In other words, if we employ a thorough system of chemical analysis with the optical apparatus, we shall be able to answer all questions lying within the range of possibility. It is this analysis applied to objects under the Microscope that we designate by the word micro-chemistry. I have endeavoured to successively make the reader acquainted with the most valuable reagents used in micro-chemistry, i.e., with those substances whose action on the bodies to be studied allows their chemical composition and nature and sometimes their physical structure to be recognized. In the first section I have considered the chemicals used in the laboratory; in the second, the vegetable substances to be tested for, and the reactions by which they are known . . . At the close of the first section I have introduced a short chapter on media for the preservation of permanent preparations, to which are added a few words on the cements used in mounting." The book ought to be in every microscopist's library. *Bot. Ztg., xli. (1883) pp. 601-6. |