more than half an hour, the rotation ceases: the motion of the spermatozoa lasts somewhat longer, but is less active, and they also eventually become quiescent.

After the spores have been in contact with the spermatozoa the former become clothed with a plainly visible membrane,* and shortly afterwards septa are formed and germination commences. Those spores which have not been in contact with spermatozoa remain unchanged for some days and ultimately decompose. Sometimes a membrane is formed over them, and a kind of imperfect germination commences, but this only lasts for a few days, after which the spores decay in the same way as those in which no membrane was formed.

Fucus serratus, L. and Fucus nodosus, L. (Ozothallia vulgaris, Dene and Thur.) yielded M. Thuret the same results, except that in the latter species the contents of the sporangium form four, not eight spores as in F. vesiculosus.

The intermixture of the spores of F. nodosus with the spermatozoa of F. serratus and vesiculosus, and of the spores of the two latter with the spermatozoa of the former yielded no results, although the spermatozoa attached themselves to the spores and produced the ordinary movement of rotation. Neither could the spores of Himanthelia lorea be impregnated by the spermatozoa of Fucus nodosus or F. serratus. The spores of F. serratus, could not be fertilized by the spermatozoa of F. vesiculosus, but strange to say, on the inverse operation, i. e., when the spores of F. vesiculosus were mixed with the spermatozoa of F. serratus, the spores germinated. Upon these facts, M. Thuret observes, that F. nodosus, Himanthelia lorea, and F. serratus, are very constant in their form, whilst F. vesiculosus is extremely variable, and he thinks it not improbable that the great variability is owing to the facility with which the latter species is

occurring when spores are examined under the microscope he explains by attributing it to the concentration of a much greater number of spermatozoa than could ever be found in the same space in nature. At the same time he considers the rotation as not altogther accidental, for he found that the spermatozoa of Fucus communicated no rotation to some spores of Florideæ, which were small enough, and round enough to have been easily set in motion, and as a matter of precaution in experiments he recommends the application of a sufficient number of spermatozoa, to render the rotation manifest.

• The formation of this membrane, is said to commence six or eight minutes after the contact of the spore with the spermatozoa. See Deuxièime note sur la fecondation des Fucacées. A. S. N. 4. Ser. Vol. vii. p. 35.

hybridized by its congeners. F. platycarpus and F. ceranoides exhibit the same variability.

M. Thuret remarks, that he finds nothing to support the supposi tion of those observers who believe that the spermatozoa effect an entrance into the spore: he has always seen them on the surface, never within the substance of the spore. *

We have next to consider the division of the Chlorospermeæ or Zoospores, in which very important results have been arrived at, principally from the observations of Dr. Pringsheim.

The plant upon which some of his earliest observations were made, was the well-known Vaucheria sessilis,† which from the simplicity of its structure offers peculiar facilities for observations of this nature. From the tubular filament of which this plant is composed, two papille in close proximity are produced. One of these becomes ultimately developed into a horn-like organ, more or less spirally twisted, in the middle of which, but at no very definite point, a septum is formed, cutting off the apex from the base. The other papilla forms a lateral protuberance, at first symmetrical, but which afterwards throws out a beak-like process (rostrum), on the side turned towards the horn. A septum is then formed at the base of this protuberance, cutting it off from the parent tube. After the formation of the septum in the hornlet, minute rod-like bodies are seen imbedded in its colourless mucous contents. In the meantime an internal layer of colourless substance, called by Pringsheim the cutaneous layer, increases to such an extent, especially in the fore-part of the rostrum, that at last the membrane of the latter is ruptured, and a portion of the cutaneous layer escapes.

Just at this period the horn opens at it apex, and the contents escape in the form of very minute rod-like corpuscles, which enter the orifice of the sporangium, and penetrate the portion of the cutaneous layer which remains. After this a membrane is formed around the contents of the sporangium (which were previously bare), and thus a cell is formed, which completely fills the sporangium— the embryonic cell of the plant. This embryonic cell, which is at first green, becomes colourless, with one or more dark-brown bodies

See Ann. des Sc. Nat. Vol. vii. p. 43.

A summary of these observations was given in the Quarterly Journal of Microscopical Science, Vol. iv. p. 63, and 124.

On the same subject, see Schenk on Vaucheria, Würz. N. Z. Vol. ii. p. 201 and Nachtrag zur Kritik, &c. (Pringsheim) in "Jahrbücher für wiss. Bot." Vol. ii. p. 470.

in its interior. It then becomes detached from the parent plant by the decay of the membrane of the sporangium, and after some time suddenly resumes its green colour and grows into a young Vaucheria, exactly resembling the parent plant.

Before dismissing Vaucheria, we may mention that fifty years before Pringsheim's publication, Vaucher had suggested the sexual nature of the horns, which he considered to be the anthers of the plant through which the pollen was discharged.

Dr. Pringsheim's observations on Vaucheria, were shortly afterwards followed by those of Cohn upon Sphæroplea annulina.* This somewhat rare Conferva was found by Dr. Cohn, covering a field of potatoes which had been overflowed by the river Oder. It forms long filaments, composed of more or less elongated cellules placed end to end. The endochrome of some of these cellules becomes transformed into a number of small spherical bodies, consisting of a green substance, with some grains of starch. Each of these bodies is clothed with a delicate smooth layer of plastic matter, but not with a cellulose membrane. They are called by Cohn primordial-spores. During, or before the formation of these primordial-spores, the membrane of the cellules, in which they are contained has become perforated with minute apertures. At the same time the colour of the contents of other cellules of the same filament changes from green to a reddish-brown, and the contents themselves become transformed into an innumerable multitude of cylindrico-elongated corpuscles, which escape through small apertures in the membrane of the cellules. These corpuscles, which are in fact the spermatozoa of the plant, enter the cellules, which contain the primordial spores, by means of the apertures existing in the membrane of the latter cellules. One or two of the corpuscles attach themselves by their cilia and beak to the end of the primordial spores and remain attached, after which the latter speedily assume a true cellular membrane. Thus, as Dr. Cohn remarks, we distinguish in the component cellular tissue of Sphæroplea male cellules and female cellules, which may be called antheridia and sporangia, and we recognize the fact, that in the impregnation, if not of the Algae generally, at least in that of the Fucaceæ, Vaucheriæ, and Sphæroplea, the one essential circumstance, viz. the direct contact of spermatozoids with a primordial cell as yet devoid of

• See Ann, des Sc. Nat. xx. 4, Ser. Vol. v. p. 188.

any investing membrane. There is also in Sphæroplea, the very remarkable fact, that whilst in Fucus, the unimpregnated spores are dispersed over the surface of their thallus where the spermatozoa must come in contact with them, and whilst in Vaucheria the orifice of the antheridium almost joins that of the sporangium, the Sphæroplea have to search out a female cellule, sufficiently developed, and often at a distance, and have then to effect an entrance through narrow apertures designed for the purpose. What the force may be which guides them to their destination, Dr. Cohn pronounces to be a veritable physiological enigma.

In Edogonium and Bulbochete* impregnation is also effected by the action of spermatozoa upon the contents of the female cells or sporangia. The contents of these female cells (Oogonia of Pringsheim) shortly before impregnation part from the wall of the cell and become contracted into a globular mass, called by Pringsheim the "Befruchtungskugel," which is a membraneless rudimentary spore. An opening is formed in the wall of the oogonium, and the nature of this opening as well as the form of the rudimentary spore varies in different species. The simplest and most frequent opening is by a small oval hole in the membrane of the oogonium, formed at the same time as the rudimentary spore. The portion of the latter which adjoins the opening is covered with a colourless protoplasm, which projects as a papilla. The spermatozoon touches and becomes intermixed with the papilla, which then retracts itself into the oogonium and the impregnation of the spore is effected.

The most remarkable point in the impregnation of the Edogenies is the different mode in which the spermatozoa originate in different species. In some species of Edogonium they are produced directly from certain cells which are true antheridia-the antheridia and oogonia occurring in most cases upon separate plants, but in some instances upon the same plants. This is quite similar to what occurs in other Algæ. But in other species of Edogonium, and in most, if not all, of Bulbochate, the antheridia are produced by certain bodies to which M. Pringsheim has given the name of androspores. These androspores are produced in cells differing from the ordinary vegetative cells only in their small size. The androspores differ hardly at all from the ordinary zoospores of the plant except in being of smaller size, and after their escape from the parent cell they

* Sce Jahrbücher für wiss. Bot. Vol. i. p. 1.

swim about freely in the water. They are oval, nearly filled with a green substance, but having a transparent beak surrounded by cilia. After some time the androspores attach themselves by the beak to the oogonia, the cilia fall off, and they then commence a true vegetative growth and become transformed into an organ which produces spermatozoa. In some cases the cavity of the androspore gives immediate birth to two spermatozoa; in other cases a septum is formed dividing the androspore into two cells, the upper one of which produces two spermatozoa: in other cases again several septa are formed giving rise to several cells in each of which cells two spermatozoa are produced.*

The point to which we have alluded in speaking of the Fucacesviz., whether impregnation is effected by contact merely, or whether the spermatozoa are absorbed in the rudimentary spore has been much discussed in the case of the Edogonies. Pringsheim, De Bary, and Petrowski being ranged on the one side, and Vaupell on the other.

In the Jahrbücher für wissenschaftliche Botanik, Vol. ii. p. 1-36, Dr. Pringsheim gives the results of his observations on the genus Coleochate. Here again we meet with oogonia and spermatozoa, the former being impregnated by the latter so that the sexuality of these plants also may be considered to be established.+

With regard to the nature of the Saprolegnieæ much difference of opinion has existed and still exists, some botanists considering them to belong to the Fungi, others to the Algæ. Mr. Berkeley's opinion (and none could be more valuable) was, and we believe still is, in favour of their being submerged conditions of mucedinous Fungi, but we think the majority of botanists still rank them as Algæ. However this may be, the observations of Pringsheim and De Bary show that impregnation is effected by the operation of active spermatozoa upon membraneless "primordial spores," a process precisely analogous to what we have already stated to take place in Fucus, Edogonium, and Sphæroplea. We have not space to enter into details with regard to the structure of the oogonia and antheridia, but it is worthy of remark that in all the three genera of the family-viz., Saprolegnia, Achlya, and Pythium, the spermatozoa reach the contents of the oogonia (i.e., the so-called primordial spore)

* In Edogonium curvum, Pr. it appears that only one spermatozoon is produced in each antheridial cell.

† On the peculiarity of the fructification of the Coleochateæ and their relations to the Mosses and Characeæ, see the papers above cited, pp. 24-29.

See Jahrb. für wiss. Bot. Vol. i., p. 284, Vol. ii. pp. 169 and 205.