MARINE AUJ.E OF NEW ENGLAND. 121 



-'Hcios of C<iUithiimHion, as horo umlcrstoixl. tho procumluMit filainonrs are wanting; ttr 

 miKTtVctly iloYeloiKMl. ami tho erect filniiioiits cither remuiii thnm^jhotit iuoijosii»ho. 

 nous, that is coriiposeil of sinj^jlo rows of cells, or become corticated hy the growth of 

 tlescendiug filameuts, which proceed either from the bai*e of the branches or from 

 the cells of the main filaments. The false cortication forme<l by the interlacing of 

 these lilaments is precisely analogous to what is found iu somo species of Kctocarpus 

 lud related genera. The filaments in Callitbamnion arc either all indeterminat4} in 

 growth, or else, as in the subgenus Antithamnioti^ they are of two kinds; the main tila- 

 nients being indefinite and the branches definite, so that we have inch-tinitely elongating 

 stems clothed with short, definite branches, or, to use the expression of Na*geli, with 

 leaves. The antheridia are generally in the form of short tufts of hyaline cells, 8itnat«-d 

 .>ii the npiM?r branches. In the present genus it is not rare to find species in which 

 intheridia, cystocarps, and tetraspores are borne on the same individuals, a union 

 rarely to be seen in the Floridea'. 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 col«>r 

 and grows upwards into a very long trichogyue. The antherozoids unite with the 

 tip of the trichogyne, and the fertilizing iullueuce is projjagated through the tricho- 

 gj-ue and the cells at its base to the two lateral peripheral cells, which then enlarge 

 lud divide on opposite sides of the axis and form eventually a bipartite favella. The 

 U'trasiK)res are either tripartite or cruciate. In the subgenus Seirospora there is a 

 form of non-sexual spore known as seirospores, iu 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 CaUithamnion are not well 

 dedned. 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. Balleyi, C. byssoideum, C. coryuiho- 

 8utn, and perhaps others might be iudelinitely split up, but we have preferred to adopt 

 the opposite vil'w. Within certain limits collectors may be expected to make out our 

 species of CaUithamnion, but it must often happen that forms are found which cannot 

 with certainty be referred to any of the described species. That such fonus are, as a 

 rule, new species cannot be accepted, but botanists having large sets of species of the 

 present genus soon l>ecome very liberal iu the interpretation of specitic limitations. 



Subgenus RHODOCHORTON, N;eg. 



Froiuls coiiiposLMl of procumbeut fihimcnts, from which arise vertical 

 mouopoilial lilaments ; corticatioiis wanting ; tetraspores cruciate. 



C. Ptoxnii, Lyngb. {Rhodochorton Eothii, Xivg.— TAamwuZ/w/M Rothii, 

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

 Figs. 1-2.— C. Rothii, Phyc. Brit., PI. 120 b.) 



Fronds forming indefinite patches half an inch high, vertical filaments 

 slender, naked below, bearing a few erect, appres.sed branches above, 

 which ])i^ome at the time of fnictificatiou congested and coiymlx)se, 

 bearing at their lips cruciate tetraspores; antheridia ami cystocarps 

 unknown. 



Forming dense velvety ])at(li<-s on rocks between tide marks. 



