142 



SEAWEEDS 



form of its fronds. These are chains of incrusted 

 segments jointed together cactus-fashion, and the 

 shape of the segments varies with the different 

 species, but is usually more or less heart- or 

 kidney-shaped or irregularly round. These chains 

 usually arise from cylindrical incrusted stalks, and, 



i ' 



FIG. 40. a, Udotea Favonia half natural size ; b, the same in longitudinal 

 section highly magnified. 



like the other genera, are firmly rooted by a mass of 

 rhizoids. The filaments composing the fronds are 

 dichotomously branched, but of irregular form. 

 The central ones are large and elongated in the 

 direction of the axis, while from them spring 

 shorter ones passing outwards towards the margin, 

 forming a kind of cortical zone (Fig. 416). 



