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, 
Fic. 40.—a, Udotea Pavonia half natural size ; b, the same in longitudinal 
section highly magnified. 
hke 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 clongated in the 
direction of the axis, while from them spring 
shorter ones passing outwards towards the margin, 
forming a kind of cortical zone (Fig. 410). 
