OF ARTS AND SCIENCES. 59 



matophores (cf. Fig. G). As the ramellus elongates, the proximal 

 cells gradually become somewhat swollen. They are finally broadly 

 spheroidal in shape, filled with a reticulated mass of protoplasm and 

 with a few small lenticular-shaped chromatophores (cf. Fig. 7). This 

 causes them to appear as large and transparent sacs, forming a 

 stratum adjoining the axis. As we go toward the outer end of one 

 of the more adult ramelli, the cells grow smaller, they possess more 

 abundant and larger chromatophores, and hence the outer strata of 

 cells app.ear denser and darker colored. The transition from one 

 stratum to the other is in most cases decidedly abrupt. This ap- 

 pearance of an inner transparent layer, sharply defined from an outer 

 dark layer, is visible to the naked eye. In rather old portions of 

 the plant, the very end cells, which in such places are of course 

 very numerous, become elongated and cylindrical, and so appear to 

 clothe the frond with a layer of fine filaments. 



During their growth, the branchlets of the ramelli intertwine with 

 the branchlets of the ramelli both, of the same and of adjacent whorls, 

 and this takes place to such an extent as to form a dense mass of 

 cells about the axis, separated from it by a small space, and connected 

 with it only at the nodes by the basal cells of the ramelli. We have 

 thus a hollow cylindrical frond formed about the axis, composed of 

 two sets of cells, much resembling the structure in the fronds of 

 certain species of Lemanea. When a portion of such a frond is 

 crashed, the peripheral wall of the cylinder separates, and leaves the 

 axis in pieces of considerable size. 



But before this cylinder is fully formed, and even as soon as the 

 internodal cells have elongated sufficiently to separate well the whorls 

 of ramelli, another complication of the structure arises. Filaments 

 are given off from the basal cells of the ramelli, which differ de- 

 cidedly in appearance from the ramelli arising from the same cells. 

 While the ramelli are more or less moniliform and regularly di- or 

 trichotomously branched, these filaments are uniformly cylindrical, 

 and for the greater part simple. While the ramelli grow outwards 

 and away from the axis, these new secondary filaments have a down- 

 ward course, and apply themselves closely to the axis, twining about 

 it in such a manner as finally entirely to hide the cells of which it is 

 composed. Some of these secondary filaments may originate from the 

 more distal cells of a ramellus, and in the older portions, many of them 

 thus arising may grow obliquely outwards, as well as downwards. 

 In very old stems, it frequently happens that several of these filaments, 

 intertwined so as to form a strand, proceed obliquely downwards 



