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120 THE MARINE ALGÆ OF NEW ENGLAND. A large order of filamentous algæ, many of which are monosiphonous throughout, while others are corticated either throughout or partially. The position of the antheridia and tetraspores varies in the different species. The cystocarp is a favella, which is either naked or surrounded by an involucre arising from the cells below the carpogenic cells. In cases where the frond consists of an axis with dense whorls of branches the favellæ may be partly concealed but not really immersed in the frond. The order is tolerably distinct. The fronds resemble closely those of the Wrangelieæ, and on the other hand the order passes gradually into the Cryptonemieæ by the genera Gloiosiphonia, Calosiphonia, and Nemastoma, in which the fruit is properly a favella, but is immersed in the comparatively dense outer portion of the frond instead of being free as in the Ceramieæ. In fact, it is difficult to say in which suborder Gloiosiphonia should be placed. 1. Tetraspores external, occupying the place of a branchlet or ultimate cell .... 3 2. Tetraspores wholly or partly immersed, formed from the corticating cells .. 4 3. Fronds filamentous, monosiphonous, or with a false cortex composed of descending filaments, favellæ naked or with only a rudiment ary involucre........... Callithamnion. Fronds filamentous, monosiphonous, dichotomous, favellæ involucrateGriffithsia. Fronds filamentous, branches densely whorled on the axis, favellæ involucrateHalurus. Fronds compressed, corticated, decompound-pinnate, favellæ involucratePtilota. 4. Fronds filamentous, monosiphonous, cortications at the nodes and extending over the internodes .................................................................................................... Ceramium. CALLITHAMNION, Lyngb. (From καλλος [kallos], beauty, and θαµνιον [thamnion], a small shrub.) Fronds filamentous, branching, filaments either monosiphonous throughout or becoming corticated by the growth of descending, rhizoidal filaments; antheridia forming hemispherical or ellipsoidal tufts on the branches; cystocarps composed of irregular masses of roundish spores covered by a gelatinous envelope (favellæ); tetraspores tripartite, cruciate, or polysporic; seirospores present in some species. A large and beautiful genus, of which nearly 150 species have been described. Although the genus had been divided into a number of smaller genera, the number of species still retained in Callithamnion proper is large. Nægeli, in his paper on the Morphology of the Ceramiaceæ, divides Callithamnion into a number of genera and subgenera, but we have thought best to retain the genus in an extended sense, regarding Nægeli’s division as subgenera. Spermothamnion, included by Nægeli in Herpothamnium, has been separated because the cystocarpic fruit is not strictly a favella as in Callithamnion proper. Seirospora is still retained, although it is possible that it could safely be separated as a distinct genus. The frond in Callithamnion is composed, in the beginning, of rows of cells arranged in branching filaments. In the subgenus Rhodochorton, whose relative position is doubtful because the cystocarps have not yet been observed, there are procumbent filaments, from which arise vertical branching filaments. In the other
REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 121 species of Callithamnion, as here understood, the procumbent filaments are wanting or imperfectly developed, and the erect filaments either remain throughout monosiphonous, that is composed of single rows of cells, or become corticated by the growth of descending filaments, which proceed either from the base of the branches or from the cells of the main filaments. The false cortication formed by the interlacing of these filaments is precisely analogous to what is found in some species of Ectocarpus and related genera. The filaments in Callithamnion are either all indeterminate in growth, or else, as in the subgenus Antithamnion, they are of two kinds; the main filaments being indefinite and the branches definite, so that we have indefinitely elongating stems clothed with short, definite branches, or, to use the expression of Nægeli, with leaves. The antheridia are generally in the form of short tufts of hyaline cells, situated on the upper branches. In the present genus it is not rare to find species in which antheridia, cystocarps, and tetraspores are borne on the same individuals, a union rarely to be seen in the Florideæ. The cystocarps are often binate, which is easily understood if one considers the structure of the procarp, which is formed as follows: One of the cells of the young branches enlarges and is then divided by partitions parallel to the length of the branch into a central or axial cell and a number of peripheral cells, generally four. One of the peripheral cells is then divided into an upper and one or more lower cells by a transverse partition, and the upper cell then loses its color and grows upwards into a very long trichogyne. The antherozoids unite with the tip of the trichogyne, and the fertilizing influence is propagated through the trichogyne and the cells at its base to the two lateral peripheral cells, which then enlarge and divide on opposite sides of the axis and form eventually a bipartite favella. The tetraspores are either tripartite or cruciate. In the subgenus Seirospora there is a form of non-sexual spore known as seirospores, in which at the extremity of the branches are formed tufts composed of chains of oval bodies, each one of which is capable of germinating. As is apt to be the case in a large genus, the species of Callithamnion are not well defined. Certain groups of species are distinct, but writers are not agreed as to the limits of the species in each group. By some a great many species are allowed which others regard as mere varieties. On our coast C. Baileyi, C. byssoideum, C. corymbosum, and perhaps others might be indefinitely split up, but we have preferred to adopt the opposite view. Within certain limits collectors may be expected to make out our species of Callithamnion, but it must often happen that forms are found which cannot with certainty be referred to any of the described species. That such forms are, as a rule, new species cannot be accepted, but botanists having large sets of species of the present genus soon become very liberal in the interpretation-of specific limitations. SUBGENUS RHODOCHORTON, Næg. Fronds composed of procumbent filaments, from which arise vertical monopodial filaments; cortications wanting; tetraspores cruciate. C. ROTHII, Lyngb. (Rhodochorton Rothii, Næg.—Thamnidium Rothii, Thuret, in Le Jolis’s Liste des Algues Marines de Cherbourg, Pl. 5, Figs. 1-2.—C. Rothii, Phyc. Brit., Pl. 120 b.) Fronds forming indefinite patches half an inch high, vertical filaments slender, naked below, bearing a few erect, appressed branches above, which become at the time of fructification congested and corymbose, bearing at their tips cruciate tetraspores; antheridia and cystocarps unknown. Forming dense velvety patches on rocks between tide-marks.
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I.-THE MARINE ALGÆ OF NEW ENGLAND.
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REPORT OF THE COMMISSIONER OF FISH
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