22. The second form is much more simpla, and consists of a globular or ovoidal cell, con taining in its interior a central granular mass, which, as the organ arrives at maturity, divides into four smaller quadrant-shaped spores, which finally escape by- the rupture of the cell wall. This organ is called a tetraspore ; it takes its origin in the cortical layer. The tetraspores are arranged either in an isolated manner along the branches, or in numbers to gether, surrounded by a whorl of smaller branchlets. In some cases the form of the branches which contain tetraspores is so com pletely modified by their presence, that they assume the appearance of special organs, which are called stichidia, as, for example, in Dasya.* 23. It is with respect to the third kind of reproductive organ, the antheridium, that the greatest differences of opinion exist; all observ ers, however, agreeing as to the general sig nification to be attached to it. The antheridia are always produced on different individuals, but in precisely the same situations as the tetraspores and polyspores. They are " ag glomerations of little colourless cells either united in a bunch, as in Griffithsia, or enclosed in a transparent cylinder, as in Polysiphonia, or covering a kind of expanded disc of peculiar form, as in Laurencia."1. According to the researches of Derbes and Nageli §, each of these cellules contains a spermatozoid. Mgeli describes it as a spiral fibre, which, as it escapes, lengthens itself in the form of a screw. Derbes, on the other hand, describes it as " a hyaline globule, furnished with a flagelliform appendage, by means of which it agitates itself with a very active motion, which lasts for some moments." According to M. Thuret, who certainly is to be considered a higher authority than either of the above men tioned, each cell of the antheridium is occupied by a hyaline corpuscle, spherical in Polysi. phonia, ovoidal in other genera. These cor puscles, however, whose contents are granular, offer no trace of a spiral filament, but are ex pelled from the cells by a slow motion, which Thuret compares to that observed in the ex pulsion of the tetraspores from their theca. The antheridia appear in their most simple form in Calithamnion, being reduced to a mass of cells, composed of numerous little bunches, which are sessile on the bifurcations of the terminal branches. The woodcut represents the antheridium of Griffithsia, in v. hich species, it is produced like the tetraspores, in a sort of lateral involucre of verticillate branchlets. Each of these bifurcates, and bears at the bifurcation a pyramidal antheridium, which is composed of little bunches of hyaline cells, which are arranged round a central axis, consists in the budding out of the central cell at its apex so as to form a single tubular stalk, just as in the lower Algm.
25. The antheridium of Chara is an orange red, and globular body, which is attached to the stem immediately below the germ-producing organ. It consists of eight concave, rectan gular valves, joined at their edges so as to form a hollow sphere. At each suture there is a partition, which is directed to the centre of the sphere ; while from the centre of each valve there springs a cylindrical cell, the axis of which is perpendicular to its inner surface, so that each cell approaches the centre of the sphere by its extremity. The whole anthe ridium is supported by a ninth cylindrical cell, which is inserted by its base into the stem of the plant, and passing up between the corners of the four inferior valves, approaches the other eight cylindrical cells at the centre. From the extremities of the nine cells, there emanate a number of flexible tubes, which are formed of larger cells placed end to end. At the junctions of these, smaller branches are given out, upon which the hyaline cells are sessile. These last possess a diameter of about yersr, of an inch.
From the above details it will be seen that great difficulties lie in the way of a comparison between the reproductive organs of the Flo ridem and those of other families. Nageli
considers them to present a strong analogy with those of the Hepaticm, with which he places the Floridem in a parallel position. We shall see, as we advance, how little ground there is for such a view.
The Floridem are trieecious plants : the tetraspores, polyspores, and antheridia being never found together in one individual.
24.. Characece.— Although we are well ac quainted with the structure of the reproductive organs of the Characem, we are, as yet, able to perceive only subordinate relations between them and those of other plants. These organs are of two kinds ; the one being destined to the production of a germ, the other to that of antherozoids. The former is an oblong oval body, which is placed at the junction of two segments of the articulate tubular stem. It consists of an oval germ-cell, invested by two envelopes. The outer of these is remarkable for the arrangement of the five tubular cells of which it is formed, which are twisted spirally round the central parts, and form by their ends, at the summit, a crown of five teeth.
The germination of Chara has been ob served and described by Voucher.* The de velopment of the germ, which ripens in autumn, does not take place until spring. It divided by transverse partitions into a number of segments. In each segment or cavity an antherozoid is contained. Each antherozoid is a spirally coiled fibre endowed with a power of active motion, which is displayed as soon as it is removed from its cell. The motion is of two kinds—of progression, and of revolution round the axis. According to Thuret, two cilia emanate from each antherozoid, a little behind its anterior extremity, and it is to these organs that the motion is to be attri buted.* 26. Sunzmary.—lf we take into consideration only those families of the Algae in which the phenomena of reproduction have been more or less completely investigated, we shall find that all the instances of the occurrence of bodies to which the term " germ" may be applied in the sense of the definition given at the outset, may be included in one of two classes. The first comprises zoospores and zoosporoitl bodies ; the second, all those forms of germ which re quire for their development a previous combi nation of two parts or (weans, complementary to each other as regard; their reproductive functions.
27. Zoospores.—Of zoospores we recognise two kinds, simple and ag,,,,,,regate. The simple zoospore is a pear-shaped or ovoidal body : it is composed of transparent, colourless homo geneous plasma, throughout the whole of which, with the exception of the smaller end (rostrum), granules of colouring matter are scattered. It possesses no investing mem brane, but is provided with a pair of cilia, the directions and positions of which differ accord ing to the class. Every zoospore possesses a single granule of a red or reddish-brown colour, which is always placed in the immediate neighbourhood of the colourless rostrum. Its characteristic motion is a constant prog,ression in the direction of its axis, around which the whole zoospore at the same time revolves, the transparent rostrum being always directed forwards. As regards the chemical composition of the zoospore, the transparent and colourless plasma is a nitrogenous compound, coloured brown by iodine. The cilia, as far as their reactions can be ascertained, resemble the plasma from which they emanate. As to the constitution of the coloured granules which are scattered throughout the plasma, we have as yet no direct observations ; but from the form which they exhibit being that which is always assumed by starch, not only among the Algm, but also in the green Infusoria, there can be little doubt that they are composed of that principle, in mechanical combination with colouring matter and a fat.