form sometimes assuming a convexo-concave shape. If the original form is maintained, this is effected by longitudinal ribs. The number of pores has no systematic value; the development of spines and other emergences depends on the law of the greatest economy of space. The pores are so arranged that at least one always comes into contact with the stigmatic fluid. When there is only one pore, this is a compensation to the abundant development of pollen as a protection against self-fertilization.

Fertilization of Philodendron.*-E. Warming describes the phenomena connected with the fertilization of Philodendron bipinnatifidum, belonging to the Aracea. The period of blossoming extends over from 34 to 36 hours; about 7 P.M. on the first day a great increase in temperature takes place in the staminodes and male flowers, to the extent of 18.5° C. excess over that of the surrounding air; no increase of temperature takes place in the female flowers; between 9 and 10 A.M. the next morning a second rise takes place to the extent of from 5° to 7°. About noon of the first day an aromatic odour is perceptible, and towards noon of the second day there is an abundant exudation of an aromatic sap. The anthers open between 4 and 5 P.M., and about 7 the blossoming is at an end. The author considers that fertilization is effected by pollen from the same spike, carried by small black bees, not by snails, as has been supposed.

Fertilization of the Prickly Pear.t-Dr. R. E. Kunzé sees in the irritable stamens of Opuntia vulgaris, a provision for securing cross fertilization by insect aid. In fair weather each flower opens on two successive days. Hive-bees, flies, and humble-bees were seen to visit the flowers for nectar, in obtaining which they grasp clusters of stamens, which, when released, fly up against the pistil, from which they slowly recede to their former position. Although the legs of the insects were covered with masses of pollen after visiting a flower, they were not seen to creep over the stigmas. The pollen-grains are therefore supposed to be thrown between the stigmas after the sudden movement of the stamens following the retreat of an insect. It is hardly necessary to add, however, that crossing is well effected by the insects in question, the motion of the stamens insuring a thorough dusting of their bodies with pollen.

Annual Development of Bast.-C. Hielscher has examined twenty-six different dicotyledonous and coniferous trees with respect to the amount of fresh bast formed each year. He finds that it does not consist of such well-marked regularly recurring zones as the wood in its annual rings. The primary bast always consists of both hard and soft bast; the secondary bast, formed every year, has usually the same composition, though in some cases, as Alnus and Fagus, after the second year soft bast only is developed. The amount of bast produced annually consists of three or more tangential rows of soft bast-cells.

* Engler's Bot. Jahrb., iv. (1883) pp. 328-40. See Bot. Centralbl., xv. (1883)

p. 372.

† Bull. Torrey Bot. Club, x. (1883) pp. 79-81. Cf. Science, ii. (1883) p. 381. Abhandl. Naturf. Gesell. Halle, xvi. pp. 113-39.

Independently of the layers, probably functionless, which lie above the cork, the number of zones of active bast is only small. The increase amounts at most to 1/5, usually to not more than from 1/10 to 1/20 of the total increase of the wood.

In order to distinguish between hard and soft bast the author employs anilin sulphate, which stains yellow the elements of the hard bast only. The hard bast appears to be formed first out of the cambium. On each ring of wood, two zones of bast are often formed annually, but one only, or more than two, are not uncommon. the older stems of many plants the formation of groups of sclerenchymatous cells in addition to bast-fibres is frequent.

In

Lenticels and the mode of their replacement in some woody tissues.-H. Klebahn adopts Stahl's classification of the lenticels of dicotyledons and conifers under two types, viz :-(1) those composed of loose cork-cells with denser intermediate striæ, and (2) those with closely packed cork-cells without intermediate striæ. The former kind occur in Sophora, Robinia, Alnus, Betula, Crataegus, Sorbus, Prunus, and Esculus; the latter in Gingko (Salisburia), Sambucus, Lonicera, Euonymus, Cornus, Salix, Myrica, and Ampelopsis. In both cases he regards the function of the lenticels to be as organs of aeration, to promote both the interchange of gases and transpiration.

The author then investigates by what means this function is performed in those climbing shrubs which are destitute of lenticels, and finds, in all cases, in the medullary rays, a number of parallel intercellular spaces running in a radial direction through the wood, cambium, and cortex. They are in communication with the intercellular spaces of the wood on the one hand and of the primary cortex on the other hand, and form a very efficient system of aeration for the wood.

Gum-cells of Cereals.t-Johannsen objects to the term "gumcells" (Kleberzellen), applied by Hartig to certain cells in the grains of cereals. On examining thin sections which had been preserved for years in alcohol, he found in these cells a very evident protoplasmic network or system of chambers, the contents of which, probably drops of oil, were soluble in alcohol. Sections of dry grains of wheat, rye, and barley examined in water show in these cells numerous round strongly refringent bodies of nearly uniform size, and larger drops, clearly of oil. Both are stained brown by osmic acid, but only slowly yellow by iodine-water. They consist of oil.

Separate portions of the protoplasmic network were also examined, the meshes of which were nearly as large as the smallest drops of oil. Sometimes they are also stained by osmic acid, and therefore contain oil. The sections were heated for a day or longer with absolute alcohol containing 2 per cent. of corrosive sublimate, when nothing but a protoplasmic network was always left behind, coloured by iodine or anilin-blue.

Since even the most soluble proteinaceous substances become

*Ber. Deutsch. Bot. Gesell., i. (1883) pp. 113-21 (1 pl.).

Meddel. Bot. Foren. Kjöbenhavn, 1883. See Bot. Centralbl., xv. (1883) p. 305.

insoluble on treatment with alcohol and corrosive sublimate, the author considers it probable that the "gum-cells" do not contain albuminoids, but drops of oil imbedded in a protoplasmic network, and proposes for them the preferable term " oil-cells" (Fettzellen).

Nucleus in Amylaceous Wood-cells.-B. Schorler has investigated the structure of the nucleus in the starch-containing cells of a large number of trees and shrubs belonging to different natural orders. He finds a nucleus universally present in living cells, although of so delicate a nature that it is often not visible except by hardening and staining. Its form is originally spherical or ellipsoidal; but external forces subsequently bring about a great variety of changes. The size also varies very greatly; it is on the average larger in Coniferæ than in dicotyledons. The measurements are given of the nuclei in a great number of species, the length varying from 3 to 25.5 μ; the breadth from 1.5 to 13.5 μ; while some are nearly as broad as long, in others the length is ten times the breadth. The internal differences are but comparatively small, as shown by the different degrees in which pigments are taken up. One or more nucleoli may be present, and a nuclear membrane can usually be detected.

Even in mature wood-cells the nuclei are often not only in a living eondition, but are even capable of division. The nucleus may remain unchanged so long as starch is still stored up in the cells. In the older rings of wood they may even retain their vitality for a period of eighty-six years (Sorbus torminalis), or even longer. When dead the nucleus does not necessarily disappear, it may become disorganized by a complete change in its internal structure, exhibited by its losing its granular character and becoming rigid, frequently in consequence of becoming permeated by resin. Such nuclei, of a dark brown colour, have been found in the 110th annual ring of the yew.

Peculiar Stomata in Coniferæ.t-K. Wilhelm describes a peculiar structure of the stomata in the leaves of Abies pectinata, the outermost cavity of the stoma containing, at all times of the year, a number of nearly black patches composed of a great quantity of minute granules. The particles are nearly insoluble in cold, but very soluble in hot alcohol, and are of the nature of wax, apparently identical with that which covers the surface of the leaves. Their purpose is apparently to hinder transpiration. This peculiar substance appears to be invariably present in the stomata of Abies pectinata, and in many other Abietineæ and Cupressineæ, but was not found in the yew.

Root-hairs.-F. Schwarz publishes an exhaustive account of the root-hairs of plants in their morphological and physiological relations. Although it is possible in certain cases for roots to absorb nourishment from the soil when destitute of root-hairs, yet the latter are unquestionably the most important organs for this purpose. The

Jenaisch. Zeitschr. f. Naturw., xvi. (1883) pp. 329-57.

† Ber. Deutsch. Bot. Gesell., i. (1883) pp. 325-30.

Unters. Bot. Inst. Tübingen, i. (1883) pp. 135-88 (1 pl.). See Bot. Centralbl., xv. (1883) p. 337.

increase of surface brought about by root-hairs as compared with that of naked roots at from 5.5 to 18.7.

The root-hair has a constant tendency to grow in a downward vertical direction; when this is interfered with by any solid body, it grows along this body until it can again resume its original direction. A close attachment to the particles of soil is increased by the mucilaginous character of the outermost cell-wall. They are formed only at a certain distance from the apex of the root, in order not to interfere with the hydrotropic and geotropic movement of the latter. The external condition which affects more than any other the formation of root-hairs is the degree of moisture; too little and too much moisture are equally unfavourable. A retardation of growth from too much moisture goes along with a reduction of the amount of roothairs; a retardation of growth from too little moisture causes a local increase of root-hairs, though the total quantity may be diminished.

The suppression of root-hairs in many water-plants is not due to the smaller supply of oxygen, but to other causes not altogether known at present; some water-plants form root-hairs abundantly when their roots penetrate into mud or soil.

Entire suppression of the root-hairs occurs in only comparatively few plants, not connected genetically, but related only in their mode of life. They are nearly or altogether purposeless in such as have a very abundant supply of water, as many bog- and water-plants, like Butomus, Caltha, Euryale, Lemna, Nymphaea, &c., and in those which, owing to their very small power of transpiration, require but very little water, as many Coniferæ, Agave, Phoenix, &c., from which they are altogether absent. They occur, however, in some succulent plants, as Crassulacea and Cactaceae; in the bulbous and tuberous Liliacea they are present or absent according to their habit. Parasites usually have root-hairs when they also have the power of growing independently, as Euphrasia and Melampyrum; Rhinanthus, parasitic on the roots of grass, is destitute of them; many saprophytes, as Monotropa, Neottia, and Orobanche, are entirely wanting in root-hairs.

A great increase in the quantity of root-hairs may take place for a specific purpose, and organs of different value morphologically may become covered with them. They occur, for example, on the coleorhiza of Myrtacea, Scabiosa atropurpurea, and some grasses, for the purpose of fixing the seedling firmly in the soil. In Psilotum triquetrum, Corallorhiza innata, and Epipogon Gmelini, they are produced on the cauline organs, which perform the function of roots.

The root-hair is almost always simply an outgrowth of an epidermal cell. In exceptional cases the mother-cell subsequently forms a sheath round it, as in the prothallium of Alsophila australis and Aspidium molle. They are developed acropetally without any definite arrangement; rarely, as in Nuphar, Elodea, &c., they arise out of cells already formed. Their form does not vary greatly, though they are to a certain extent affected by external circumstances, contact, food-supply, &c. They may occasionally branch, and even twine. The longest root-hairs observed by the author were those of the Marchantiaceae, 18 mm., Trianea, 8 mm., Potamogeton, 5 mm., and Elodea, 4 mm.

Sieve-tubes of Cucurbita.*-According to A. Fischer, a transverse section of an internode of Cucurbita shows two systems of sieve-tubes, one belonging to the vascular bundles, and the other situated within the sclerenchymatous ring so characteristic of the Cucurbitaceæ, which lies beneath the strongly developed collenchymatous tissue. This occurrence of sieve-tubes in the cortex is, as far as is at present known, entirely confined to this order. The sieve-tubes of the separate vascular bundles are united into one system with one another and with those of the cortex for the conveyance of nitrogenous formative materials, by fine transverse uniting strings which press through the fundamental tissue. On the other hand the peripheral sieve-tubes can only be in communication with this system through the nodes, as no uniting strings have been observed to pass through the sclerenchymatous ring, which is closed on all sides.

Spines of the Aurantiaceæ.-J. Urban has investigated the morphological value of the spines, which occur singly or in pairs, in the axils of the leaves of many but not all Aurantiaceæ, and which have been generally regarded as metamorphosed axillary shoots. From comparison with unarmed species, and from the history of development, Urban regards them, on the contrary, as the metamorphosed lowermost leaves of the primary axillary shoot. Intermediate forms are exhibited by some species of Citrus.

Tubers of Myrmecodia echinata.‡-M. Treub describes the remarkable tuberous stem of the epiphytal Rubiaceous genera Myrmecodia and Hydnophytum, which are permeated by passages inhabited by immense numbers of ants. He states that the passages are not burrowed by the ants, but are formed by the disappearance of cells which become entirely enveloped in layers of cork. Their object is not to protect the colonies of ants, or to supply them with food, but rather to facilitate communication between the inclosed air-spaces and the external atmosphere.

Chlorophyll-grains, their Chemical, Morphological, and Biological Nature.§-A. Meyer continues his previous investigations on this subject.

He expresses a strong opinion against the chlorophyll-grains being surrounded by a membrane. Where a denser portion becomes separated on contact with water, this must not be regarded as originally present; for if so, it would become thinner by the swelling of the surrounding protoplasm, or by tensions resulting from endosmotic action, which is not the case. Pringsheim's lipochlor and hypochlorin he regards as still hypothetical.

Observations on Acanthephippium and Asphodelus show that the

* Ber. Deutsch. Bot. Gesell., i. (1883) pp. 276-9.

† Ibid., pp. 313–9 (1 pl.).

Ann. Jard. Bot. Buitenzorg, iii. pp. 129–60 (5 pls.). See Bot. Centralbl., xvi. (1883) p. 103.

$ Meyer, A., Das Chlorophyll-korn, in chemischer, morphologischer, u. biologischer Beziehung' (3 pls.). Leipzig, 1883. See Bot. Centralbl., xv. (1883) p. 332.

See this Journal, iii. (1883) p. 239.

Ser. 2.-VOL. IV.

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