for the determination of species, and even in some cases of genera, but not of the larger groups, since their formation probably depends on external conditions.

Hybridism in the Conjugatæ.-C. E. Bessey describes an interesting case of hybridism between two species of Spirogyra, S. majuscula and protecta. A perfect zygospore was found, resembling most nearly those of the latter species.

New Genera of Chroococcaceæ and Palmellaceæ.†-In an account of the algae of Sweden, G. Lagerheim describes as many as sixty species new to that country; and gives also the following diagnosis of new genera :

Gleochate (Chroococcaceae). Cellulæ globosa vel subovales, binæ vel quaternæ in muco communi homogeneo vel indistinctissime lamelloso inclusæ, utraque seto longissimo instructa. Cytioplasma ærugineo-cærulea, subgranulosa. Divisio cellularum in duas directiones. One species, G. Wittrockiana, possibly identical with Chatococcus hyalinus Kütz.

Acanthococcus (Palmellaceae). Cellulæ adultæ globosæ vel subglobosa, aculeis præditæ. Divisio succedanea, multitudo cellularum filialium globosarum, non aculeatarum, in cellula matricali provenit, quæ, membrana cellulæ matricalis in mucum conversa, liberæ fiunt. Cellulæ perdurantes oleosa. Two species, one of them the Palmella hirta and Pleurococcus vestitus of Reinsch.

Dactylothece (Palmellaceae). Cellulæ cylindricæ vel oblongæ, rectæ vel leviter curvatæ, utroque fine rotundatæ, singulæ-quaternæ in familiis consociatæ, tegumentis vesiculiformibus incluse. Familiæ numerosæ hoc modo formate stratum viride uliginosum formant. Divisio cellularum in unam directionem fit. Cytioplasma viridis. Zoosporæ ignotæ. Analogous to Glæothece among Chroococcaceæ. One species, D. Braunii, in greenhouses.

Also the subgenus Holopedium:-Merismopedium familiis forma irregulari e cellulis irregulariter dispositis compositis. Divisio cellularum irregularis. Includes the three species of Merismopedium, irregulare, sabulicolum, and geminatum.

Chroolepus umbrinum.-J. B. Schnetzler finds this alga, associated with a number of others, on the bark of the vine, forming moniliform threads of globular cells about 30 μ in diameter. It also occurs in similar localities imbedded in the thallus of a lichen belonging to the genus Pyrenula. In this condition it forms filaments composed of much smaller cells. When the lichen-thallus decays, these cells escape, and, on multiplying, assume again the normal size of those of the free form.

Constant Production of Oxygen by the Action of Sunlight on Protococcus pluvialis.§-In the summer, Zygnema and Conferva may

Amer. Natural., xviii. (1884) pp. 67-8.

+ Oefvers. af Svenska Vetensk. Akad. Förhandl., 1883, pp. 37-78 (1 pl.). Bull. Soc. Vaud. Sci. Nat., xix. (1883) pp. 53-4.

§ Chem. News, xlviii. (1883) pp. 205–6.

frequently be seen borne to the surface of pools of stagnant water by innumerable minute bubbles of oxygen gas. Some of the simplest of the unicellular algæ, e. g. Protococcus pluvialis and P. palustris, exhibit this peculiarity to a remarkable degree. T. L. Phipson has cultivated some of the last-mentioned plants by exposing pump-water to air and light for some weeks, and as soon as good growth was obtained, small dead branches of poplar were put in the water; the Protococcus developed rapidly upon them. The branches can then be put in flasks full of water, and the production of oxygen observed; this takes place immediately the flasks are exposed to the sun's rays; the oxygen comes off in the minutest bubbles, but in such great numbers as to form a froth on the surface; in some higher plants, e. g. Achillea Millefolium, the gas collects at the end of the leaves, and comes to the surface in large bubbles. If the flask is inverted the evolution of gas continues for about three days; the introduction of a minute quantity of caustic soda stops it on the first day by depriving the plant of carbonic anhydride. On renewing the water after three days, the evolution recommences, and so by keeping up a constant supply of pump-water and the production of oxygen, may be kept up to all appearance indefinitely.

The author has devised a simple apparatus for this purpose. A wide-mouthed bottle with tubulure near the bottom, is fitted with a gas delivery tube, and a tube with tap connected with a water-supply; the water must neither be boiled nor distilled, nor must it be in the slightest degree alkaline. A tap is put in the tubulure and is used to empty the bottle. Some of the poplar branches are placed in the bottle, water is run in, and the bottle exposed to sunlight; the oxygen can be collected in a gas-holder. After three days the old water is run out of the bottle and fresh water run in. The author suggests that by employing graduated vessels, &c., the apparatus might be used as an actinometer. The gas produced contains about 98 per cent. oxygen. The author remarks incidentally that carbonic anhydride in presence of sunlight is not decomposed by plants, but simply absorbed, water and hydrogen dioxide being equally essential for the production of oxygen, and the gas being evolved from the tissue as a consequence of the absorption.

Chromatophores of Marine Diatoms.-O. Müller describes the peculiar form and structure of the chromatophores in some marine diatoms, hardened and coloured according to Pfitzer's nigrosin-picricacid method.

In Pleurosigma angulatum the chromatophores consist of two very long bands, twice the length of the longitudinal diameter of the cell or more, comparatively narrow, much lobed and indented, but never perforated. They are arranged symmetrically on each side of the cell. For their whole length their surface is applied to the cellwall, and separated from it by only a thin layer of protoplasm. A middle portion of each band, about one-t e-third of its entire length, runs undivided to the inner surface of the upper shell-i. e. the shell which

*Ber. Deutsch. Bot. Gesell., i. (1883) pp. 478-84.

contains the central portion of the chromatophore. Two pieces, together about equal in length to each of the middle pieces, lie separately on the lower shell, while the ends which enter the apices of the cell turn to the girdle-bands of the cell-wall, where also the pieces which start from the upper and under shells unite. The function of the chromatophore is therefore distributed nearly equally to both sides of the protoplasmic body of the cell. The median line of the chromatophore coincides, as in Navicula, with that of the girdle-bands; but the portions which project upon the adjoining cells are not arranged symmetrically in relation to the plane of division. The middle piece of each chromatophore, which lies on the upper shell, on both sides of the raphe, incloses, in the typical arrangement, the central cell-nucleus with a semicircular opening inwards.

Pleurosigma balticum also contains two chromatophores whose median line coincides with that of the girdle-bands, and which project on the shells on both sides; but they are not band-shaped and folded, as in Pleurosigma angulatum, but plates of a somewhat complicated structure. Pleurosigma Hippocampus has chromatophores of a similar form, but narrower.

Nitzschia Sigma has only a single chromatophore, which is, however, completely divided by the cell-nucleus; not so completely in other species belonging to the same group of the genus. It is plateshaped, and is applied to that girdle-band which is opposite the two points of the keel. On its median line, in each of the two halves, lie five or more round or oval pyrenoids, bodies which are not unfrequently present in diatoms. They appear here not to be of such simple structure as in other cases. They are coloured more or less dark by nigrosin, and are surrounded by a light border, which, with very high powers, exhibits a differentiation into small bright dots, the structure being therefore similar to that in the Chlorophyceæ.

Division of Synedra Ulna.*-G. Schaarschmidt has found this diatom in an active state of division; he fixed the specimens with picric acid or absolute alcohol, coloured them with hematoxylin or eosin, compared them with living specimens, and gives the following as the chief results obtained. When division commences the breadth increases by the girdle-bands becoming separated to a greater distance; but the lamellæ of endochrome retain their position, and their margins scarcely project in this condition over the girdle-bands; while, in individuals that are not dividing or only preparing to divide, they reach the end of the cells; but in those which have just divided or are dividing repeatedly, they are about 1/6 of the length of the cell shorter than the shell. The strongly refractive colourless nucleus is in the central mass of protoplasm which often lies only on one shell; no nucleoli can be detected in it. In cells which are about to divide it moves into the middle of the cell; its enveloping protoplasm, through which small mucilaginous particles are scattered, then lengthens towards the ends of the cell, where the protoplasm then Magy. Növ. Lapok, vii. (1883) pp. 49–58 (1 pl.). See Bot. Centralbl., xvi. (1883) pp. 198-9.

takes the form of an axile band uniting the ends of the cell, and concealing the nucleus in its swollen central part, which no longer touches the shells; the nucleus is now held by delicate threads of protoplasm which spring from the plates of endochrome.

While the axile band is developing thus, the plates of endochrome broaden to such an extent that they almost cover the entire sides of the girdle-bands. At this period, or even earlier, the plates, which were at first constricted, are now bisected.

At this stage of development the division of the nucleus commences. The species under examination exhibits this peculiarity, that the division of the nucleus, which now becomes of a broadly elliptical form, and breaks up immediately into two daughter-cells, proceeds in a direction parallel to the new shells. Only in a few cases are there spindle-fibres stretched between the two daughter-nuclei ; these fibres are knotted in the middle, which may be regarded as a tendency towards the formation of nuclear plates. The daughter-nuclei may divide again, so that in the middle of the axile band there are formed at length from four to seven nuclei.

When the division of the nuclei is complete, the substance of the axile band becomes firmer, commencing at the ends, and dark dots are seen in it arranged in longitudinal rows, and later, short transverse striæ corresponding to them, which, however, become gradually indistinguishable towards the centre of the band where the nuclei lie. The daughternuclei, which hitherto lay one over the other, now approach one another in a horizontal direction (in the transverse diameter of the cell), and are separated only by the axile band, which is continually becoming denser, and which now divides the cell into two halves as an extremely delicate and flexible septum. The new septum becomes further differentiated, splits, and from it are formed the new shells of the daughter-cells. This process goes on very rapidly, and the transitional steps can be readily followed from the simply punctated or striated lamella to the double lamellæ. Cells with split septum are more often met with than with simple septum; but still more often the septum shows the dots only at the ends. These dots or striæ— since the septum is turned with its narrower side towards the observer -probably correspond to the channels of the new shells.

The new septum now acquires firmness, and now the movement commences of the lamella of endochrome; of those which lay upon the old shells, those which were opposed diagonally, with their ends pointing towards the middle of the cell, creep slowly through the sides of the girdle-bands, while the other lamella remains upon the old shell, pushing itself beneath it. Delicate threads of protoplasm are not unfrequently found between the upper ends of the lamellæ and the ends of the cell. The lamellæ attain their full size very quickly after their transfer. Frequently they break up into two, three, or more pieces, which become transported in the same way as the larger ones.

The nuclei may break up in the same way by repeated constriction into a large number of daughter-nuclei; four or five nuclei are not unfrequently found in each daughter-cell. The cells of Synedra Ulni are therefore multinucleated during and after division.

Arctic Diatoms.*-P. T. Cleve describes the diatoms collected by M. Kjellman during the expedition of the Vega' from the following Sources:- -Arctic diatoms from the ice near Cape Wankarema and near East Cape; from the surface in Behring's Sea; fresh-water diatoms from Japan; diatoms from algæ collected on the island of Labuan, near Borneo; from algae and coarse bottom-mud collected near Point de Galle, Ceylon; and from bottom-mud between Aden and Bab-el-Mandeb. The Arctic material contained a very large number of species, which varied to an astonishing extent, so that in many cases it was scarcely possible to trace out the limits of the species. On the other hand, samples from the bottom of the North Siberian Sea were quite free from diatoms. The descriptions, &c., are in English, and several new species are described.

A few new species are also described by the same authority,† collected during the Arctic expedition of Sir George Nares.

Pelagic Diatoms of the Baltic.‡-A. Engler describes the pelagic diatoms gathered in the Baltic, chiefly in scum on the surface of the water in the bay and harbour of Kiel. Different times of the year are distinguished by the appearance of different genera and species. Among the more interesting forms observed was the remarkable genus Chatoceros, provided with horns or bristles from 5 to 20 times the length of the cylindrical part of the cell, the cell-contents being in communication throughout. Of this genus many species are known in the Arctic and Pacific Oceans; six are now described from Kiel Bay, one of them, C. Grunowii, new, was found with spores.

Diatoms of Lake Bracciano.§-M. Lanzì has examined for diatoms the water from the middle of this lake, and finds that, like the pelagic species, they differ from those found in shallow water. The swimming deep-water species found were Fragilaria crotonensis Edw. (Nitzschia Pecten Brun.), Cyclotella comta var. oligactis Grun., C. comensis Grun., and Asterionella formosa Hass. Those found near the shore, living on plants, stones, &c., belonged to the genera Navicula, Stauroneis, Mastogloia, Cymbella, Amphora, Cocconeis, Achnanthes, Gomphonema, Staurosira, Synedra, Epithemia, Surirella, Cymatopleura, &c.

* Cleve, P. T., 'Diatoms collected during the expedition of the Vega,' 60 pp. (4 pls.), Stockholm, 1883.

† Journ. Linn. Soc. (Bot.), xx. (1883) pp. 313-7.

Ber. Deutsch. Bot. Gesell., i. (1883); Gen.-Versamml. in Freiburg, pp. x.-xiii. § Atti Accad. Pont. Nuovi Lincei, xxxv. (1883) May 21. See Bot. Centralbl., xvi. (1883) p. 257.