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velopment, and may be expected to occur as well in one series as in another.

The arguments against the distinctness of type between Monocotyledons and Dicotyledons are thus given.-1. The form of the embryo varies much in different Monocotyledons, the radicular part sometimes being by far the largest, while at other times the cotyledon forms almost the whole embryo. The position and direction of the plumule also vary. It is therefore more probable that the monocotyledonous embryo is a mere thalloid expansion than that it is a reduced form of that of Dicotyledons with the different parts not yet differentiated.-2nd. The parts of the monocotyledonous embryo generally called cotyledon and radicle cannot be said to discharge the functions of those organs.-3rd. The monocotyledonous embryo occasionally contains several plumules or gemmae, a thing quite opposed to the nature of a cotyledon, and much more capable of explanation on the supposition that the embryo is a thalloid body. Prof. Agardh adds, "I therefore think it very useful to retain Richard's "name hypoblast, which indicates an organ in an early stage of evolu"tion, with doubtful functions, which may have one or more plumules."

This short account of the contents of a very curious and interesting work will best end with the author's own abstract of the principles from which perfection of organisation is to be inferred. "Those plants are most perfect," he tells us, "in which the organs discharging different functions are most distinct both in position and structure. The thalloid fronds (of Cactaceae) and the hypoblastoid embryos of Endogens indicate a lower degree of organisation. Plants which have the stamens and pistils either naked or in the axil of an unmodified leaf (Naias, Hippuris, Callitriche) are inferior to those whose flowers are never complicated. Diclinous flowers are lower in position than those which are hermaphrodite; ternary verticils lower than quiniary, spirally arranged floral organs lower than those which are verticillate, polypetalous flowers lower than gamopetalous, apocarpous ovaries lower than syncarpous, atropous ovules lower than those which are inverted, homogeneous embryos lower than those which are fully developed. Trees and shrubs are more common among imperfect plants. In the lower orders flowers are very numerous, in the higher the number of seeds produced by each flower is very great. Yellow and green colours on the flowers of the lowest rank are changed into red or white in those of a higher order, and in the highest plants the colour of the flower is generally blue."

LXVII. HEGELMAIER'S MONOGRAPH OF CALLITRICHE.

MONOGRAPHIE DER GATTUNG CALLITRICHE. Von Friedrich Hegelmaier, Med. et Chir. D. Stuttgardt, 1864. 4to. With 4 plates. AMONG the various weeds floating in our ponds, there is none that has excited more interest among botanists than the common Callitriche, called sometimes Water Starwort, although it has no connection with either Aster or Stellaria. Very abundant in ponds and still waters in almost all parts of the world, vegetating also in wet mud, it assumes a number of different forms, especially as to size and foliage, according to station, season, period of growth, etc., and like all common plants, has established several more permanent races, characterised chiefly by differences in the shape of the fruit. At the same time, the flowers are reduced to almost the last degree of simplicity a phænogamous plant is capable of assuming. Accordingly, it has been a subject of repeated controversy, how many species the genus consists of, estimated at any number from one to twenty, according to the individual views of botanists, and what are its affinities in the natural system-what are the types of which it is a reduced form. Dr. Hegelmaier has taken up the subject in detail in most of its bearings, he has more especially investigated the anatomical structure, and appears also to have observed and described the position and development of the ovule more accurately than his predecessors, illustrating the whole by well-executed and very clear lithographic figures. His conclusions are entirely in favour of Brown's views of the affinity of Callitriche with Halorageæ, and very much against the theory recently propounded by some French botanists, and especially by Baillon, of a close connection with Euphorbiaccæ. He insists on the ovule at the time of flowering being a naked nucleus, which in its growth has assumed the appearance only of an ordinary anatropous ovule, which Baillon and others suppose it to be in reality. With regard to the systematic subdivision of the genus, Dr. Hegelmaier judiciously rejects all characters derived from the size and shape of the leaves, the pedunculate or sessile flowers, etc. which are known to vary on the same individual, according to external circumstances. But he admits thirteen species distributed into two sections or subgenera. For these two main groups he relies chiefly upon biological characters; in Eucallitriche the flowering summits ascend to the surface of the water, and fertilization always takes place above it; in Pseudo-callitriche, the plant remains entirely under

water, in which medium the fertilization of the flowers is accomplished. These distinctions are accompanied by physiological and anatomical differences, which may be the result of external circumstances rather than correlative characters. There is, however, one carpological character, which, if proved to be constant and definite (which we are rather disposed to doubt), may be considered as sufficient to retain the two sections as distinct species. In Eucallitriche, the two carpels of which the fruit is composed are said to be always broadly united by their inner faces, in Pseudo-callitriche they are only very narrowly connected. The minor differences by which the eleven species of one section and the two of the other are separated, appear to us to be very variable, and often very difficult to appreciate, and there is in most cases nothing in their geographical distribution to support the idea of their constancy. The most remarkable form described, appears to be that of C. Drummondii, Hegelm., only known from a few specimens gathered in one locality (near New Orleans), by a single collector. But whatever be the views entertained of his systematic conclusions, Dr. Hegelmaier's work is evidently the result of careful and painstaking observations and researches.

LXVIII.-VEGETABLE SPERMATOZOIDS.

DIE SPERMATOZOIDEN IM PFLANZENREICH. EIN BEITRAG ZUR KENNTNISS DERSELBEN. Von Dr. Hermann Schacht. schweig, 1864.

Braun

THIS work is not a general treatise on vegetable spermatozoids, but contains the results of the author's observations upon certain particular plants, and gives the general conclusions to which those observations led him.

The first plant mentioned is Equisetum Telmateia, which Dr. Schacht considered to be one of the best for observations on the spermatozoids, because, although the latter are of small size they are shorter and thicker than those of most other species. For the information of those who may wish to examine these bodies, we may state that there is no difficulty in procuring the germination of the spores of Equiseta. Dr. Schacht sowed them in two glass vessels, one containing water only, and the other garden mould covered with water, so that the latter stood half an inch above the mould. The

spores in the vessel which contained only water produced small prothallia, which yielded no sexual organs. Those on the surface of the water in the vessel which had also the garden mould, yielded prothallia which were better developed and which produced antheridia, but no archegonia were formed. The spores on the surface of the mould itself produced prothallia, which yielded both antheridia and archegonia.* The latter, however, were so few in number that Dr. Schacht was unable to follow out the process of impregnation, and confined his observations to the spermatozoa.

We need not enter into his description of the antheridium and its mode of dehiscence, which are already sufficiently known from the observations of Hofmeister and others. He states that in E. Telmateia the aperture through which the mother-cells of the spermatozoa escape varies in form according as its boundary consists of 2, 3 or 4 cells. These boundary cells, if we understand rightly, are the same as those which are called by Hofmeister the " "apical cells of the covering layer."t Hofmeister states that they are usually eight in number in the species examined by him, but these species did not include E. Telmateia.

With regard to the escape of the spermatozoa from the mothercells, Dr. Schacht's opinion seems to be that under ordinary circumstances the membrane of the mother-cell is dissolved, and the spermatozoon is thus set free. He says, that the spermatozoon unrolls itself (usually without the previous gyratory motion so often observed in ferns) after the membrane of its mother-cell has been dissolved in water, and that the dissolution of the membrane of the mother-cell must be regarded as a gradual and complete dissipation of it. This, however, is not always the case, for he adds, that it does not always happen that the membrane of the mother-cell is dissolved: it is sometimes ruptured suddenly or gradually by the spermatozoon, in which case on the escape of the spermatozoon from its mother-cell, the entire contents of the latter go to form the spermatozoon, whilst the membrane remains behind in the form of a globular covering ruptured at one spot. These observations are not quite in

* A simpler plan, and one which we have found to succeed well, is to sow the spores in a small garden-pot on the surface of silver-sand thoroughly moistened, to let the pot stand in a pan of water, and cover it with a bell glass. By this means the sand is kept constantly moist, and the young prothallia are more easily taken up and cleaned for the microscope, than when growing on wet garden mould.

† See Hofmeister on the Higher Cryptogamia, Ray Society's Translation, 1862.

accordance with those of Hofmeister. The latter writer says, that the spermatozoon seldom becomes entirely free from its mother-cell, and although his (Hofmeister's) remarks do not apply to Eq. Telmateia, it is hardly probable that there should be any difference in this respect between that species and the numerous species examined by Hofmeister.

With regard to the structure of the spermatozoon, Dr. Schacht states, that it consists of a cell having a protoplasmic membrane and granular contents, that it is probably hollow throughout its whole length, and has, at least in the hinder half, one of its sides much thickened, and the opposite one very delicate. He considers this latter side to be that which forms the vesicle noticed by other observers, but that such vesicle is not (as has been supposed) always found at the hinder end. He says, that the vesicle is to be seen on different parts of the last turn of the spiral, and that it varies in shape and may even almost entirely disappear, when the spermatozoon is fully stretched out. With respect to this so-called vesicle, we would direct attention to Hofmeister's remarks in the new (Ray Society's) edition of the " Vergleichende Untersuchungen." Hofmeister clearly refers to the same part of the spermatozoon, although he differs widely in his view of the structure, when he says, "The end of the sper

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"matozoon bears on the inner side of its ultimate turn a wide fin-like process, consisting of a delicate membrane which during the motion "of the spermatozoon glistens like the undulating membranes of the spermatozoa of Toads and Tritons. When the motion becomes more active the membranous margin becomes invisible like the "cilia; it is only clearly visible when the vital activity of the sper"matozoon is on the decline."

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A singular feature, noticed in the spermatozoa of Equiseta (but which we believe is not peculiar to the Equisetacea), is the capacity of losing a portion of their substance without any apparent effect upon the vitality of the spermatozoon. Hofmeister has noticed this, and in the first edition of the "Vergleichende Untersuchungen," he spoke of the elongated form of the hinder end as a peculiarity common to the spermatozoa of Equiseta. The real fact is that the glutinous tail becomes attached to foreign objects, and by the effort of the spermatozoon to free itself, the hinder part becomes drawn out into a whip-shaped appendage. This is the explanation given by Hofmeister in his last edition, and it is confirmed by Dr. Schacht in the work before us.

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