v.r CERAMIACE^. 229 



VIII. CALLITHAMNION. Lyngh. 



Frond filifoi'm, branched, articulated, monosiphonous, the stem and branches (in 

 many species) at length rendered opaque by the development of decurrent filaments 

 in the walls of the primary cells ; ramuli always articulated, monosiphonous. 

 Favellce generally binate, axillary or sessile on the branches, naked or nearly so, 

 containing, within a hyaline periderm, numerous angular spores. Tetraspores 

 naked, sessile or pedicellate, distributed along the ramuli, oblong or globose, trian- 

 gularly or cruciately parted. 



A very large genus of beautiful Alga?, sometimes minute, never of large size, 

 rarely exceeding six inches in length. The fronds in the least developed species 

 are but shghtly branched, a line or two long, parasitical, forming a down-like 

 covering to the plants on which they grow. Others, a little more perfect, grow on 

 rocks, on which they form dense, cushion-like tufts, from a quarter inch to an inch 

 in height. Some few have their smaller branches and ramuli dichotomously 

 multifid. The greater number, however, are branched on a more or less regularly 

 pinnate type ; the pinna3 and pinnule either opposite or alternate, rising singly or 

 in pairs from the upper extremity of every internode. In some species every part 

 is exactly distichous : in others the lower branches and larger divisions spread to 

 all sides, while the lesser ones are distichous : and again, in others all the branches 

 and their subdivisions spread in every direction. In the smaller species the whole 

 frond is pellucidly articulate, composed of a single series of thick-walled, endochro- 

 matic cells arranged end to end ; and such is the structure of the young frond in 

 all. In the larger species, as the frond inci^eases in age, filaments, originating in 

 the bases of the branches, begin to be developed longitudinally in the substance of 

 the walls of the frond. At first they are few and short, afterwards numerous and 

 prolonged in a downward direction, and at last they completely fill the wall, 

 rendering it opaque and concealing the articulations completely. In the strongest 

 growing species the walls become at length very much thicker than the enclosed 

 tube, and completely filled with such decurrent filaments. 



The species are often very difficult of determination, forming numerous and most 

 puzzling varieties. They often require very copious materials to work on before 

 they can be well understood, and in some cases I labour under the disadvantage of 

 having received imperfect materials. Some of the following species present so 

 many forms, that before I had compared together very extensive suites, I was dis- 

 posed to separate into four or five what I now regard as a single species. And 

 though my friend Prof Agardh has considerably curtailed the species as described 

 by other writers, I fear that of the sixty-three which his work still admits, several 

 should be struck off. To come to right conclusions on this point, the species should 

 be studied on the sea shore, before the specimens have been dried, for the characters of 

 many are of so delicate a nature, that they are apt to be saved or lost, according as the 



