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 Laminariaceaf, &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 (Corallinece, Squamariecc, and Siphonece). 

 Stability is obtained in Caulerpa by the formation 

 of numerous trabeculse 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 



