. 
24 SEAWEEDS 
by a single apical cell, or a marginal series, or a 
meristematic group in the multicellular forms, or by 
the apical protoplasmic contents in siphoneous 
plants ; or (2) intercalary, at a definite growing-point 
in the frond, as in Laminariacew, &c., or in a 
terminal hair or tuft of hairs with a basal growing- 
point. Sometimes all the cells of the body remain 
meristematic and engaged in growth. Secondary 
growth in thickness may take place, as in the stalk 
of Laminaria, by the peripheral cells beneath the 
rind being capable. of division, and thus adding to 
the internal tissues, as well as forming towards the 
outside a bark-like rind; or by an adventitious 
process, as in Desmarestia, where the branching 
filaments grow together into a kind of pseudoparen- 
chymatous tissue, and invest the original cellular 
axis. 
The cohesion of the body is effected in various 
ways; either by the union of the cells into a 
parenchymatous tissue, or by the intertwining of 
filaments, aided in some cases by the development 
of sucker-like holdfasts called tenacula or haptera 
(Udotea, Struvea, &c.), or by incrustations of carbon- 
ate of lime (Corallinee, Squamariew, and Siphonec). 
Stability is obtained in Caulerpa by the formation 
of numerous trabecule or branching cellulose cross- 
beams, braces, or struts, traversing the interior of 
the cell-cavity from one part of the wall to another, 
and enabling this remarkable Alga to assume a 
differentiation into leaf-like, stem-like and root-like 
parts, though it consists of but one great cell- 
cavity. Intercellular spaces are most prominently 
