V. CERAMIAGE^. 207 



either dichotomously, or pinnately branched, the branches being similar to the main 

 stem, and always springing from the upper part of each internode (or articulation) 

 either from its shoulder, or from a short distance below that point. In some genera 

 a number of such filaments anastomose together so as to form a net-work or sponge- 

 like frond, each mesh of the net being usually formed by as many cells or articula- 

 tions as it has sides ; none with tliis hal^it, however, are yet known as North 

 American. In the filiform species the primary, articulated, filamentous frond has 

 either the simple structure described above, or it is more or less completely covered 

 over and rendered opaque by cortical cellules, which are sometimes developed on 

 the outer surface of the primary cell, but often formed within the thickened 

 cell-walls. The formation of such cortical cells commences at the nodes and 

 proceeds downwards, the lower part of the articulation being the last coated. 

 These cells are frequently deposited in linear series, but sometimes form a 

 honeycombed surface. In several Call'dhamnia the stem, which in the young frond 

 is pellucidly articulate, becomes as the plant advances in age gradually opaque, by 

 the development of numerous longitudinal articulatL^d filaments within the trans- 

 parent gelatino-cartilaginous cell walls. These filaments originate at the points 

 from which the branches and ramuli spring, and grow downwards toward the base 

 of the stem. They are indeed like roofs to the branches ; as if each branch sent 

 forth many fibrous roots through the substance of the stem ; and in their growth 

 they illustrate, analogically, the similar development of wood tissue from the bases 

 of leaves. In young specimens of Cal. Baileyi, the gradual progress of formation of 

 these filaments may be readily seen. 



In the more compound fronds, such as occur in the genera Ptilota and Micro- 

 claclia, no articulation is visible in the stem, because the primary articulated 

 filament is enclosed in a cellular coat, composed sometimes of many rows of small 

 polygonal coloured cellules. It is only in the very youngest parts of these plants 

 that articulations are partially visible ; but, on dissection, the monosiphonous 

 filament which characterises all the plants of this Order is found running, as an 

 axis, through every part of the frond. These opaque species therefore only difi"er 

 from the pellucidly articulated ones, by the greater development of the cortical 

 cellules. 



The concepfacidar fruit is of tlie kind called by Agardh afaucUa. It is formed by 

 the metamorphosis of one of the articulations or piimary cells of a branch ; either 

 of the terminal cell of a shortened branch, or of one of the upper cells. The cell 

 wall dilates, and becomes the transparent envelope or periderm to the spores, which 

 are formed by the repeated sub-division of the endochrome of the cell. These 

 favelke are frequently in pairs or clusters, and are either naked or surrounded by 

 short involucral ramuli. 



The tetraspores are usually tripartite, rarely cruciate, and still more rarely zonate. 

 They are very frequently external, either sessile on the sides of the ramuli, or on 

 little pedicels, in these cases originating in a transformation of the ultimate divi- 

 sions of the frond. Sometimes they are half immersed, and rarely wholly sunk 

 among the surface cellules of the compound fronds ; in these cases being formed 

 from some of the cortical cellules. 



