MAEINE ALG^l OF NEW ENGLAND. 121 



Species of GalUthamnion, as here understood, the procumbent filaments are wanting or 

 imperfectly developed, and the erect filaments either remain throughout monosipho- 

 nous, 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 fila- 

 ments being indefinite and the branches definite, so that we have indefinitely elongating 

 stems clothed with short, definite branches, or, to use the expression of Nsegeli, 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 Floridece. 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 par- 

 allel 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 tricho- 

 gyne 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. corymbo- 

 8um, 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 EHODOCHORTON, Nseg. 



Fronds composed of procumbent filaments, from which arise vertical 

 monopodial filaments ; cortications wanting ; tetraspores cruciate. 



C. Bothh, Lyngb. (Bhodochorton Bothii, Nseg. — Thamnidium Rothii, 

 Thuret, in Le Jolis's Liste des Algues Marines de Cherbourg, PI. 5, 

 Figs. 1-2.— C. RotMi, Phyc. Brit., PL 120 6.) 



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. 



