100 SEAWEEDS 
divisions of the cells of the growing point beneath 
the apex. The characteristic mantle which forms 
the secondary growth in thickness originates from 
the basal cells of the lateral branches arising directly 
below the growing point; the cell-filaments so pro- 
duced unite in parenchymatous fashion, and remain 
closely adherent to the primary row and divide in 
Fic. 24.—Desmarestia aculeata a, longitudinal section showing mantle of 
filaments ; b, transverse section, Highly magnilied. 
x 
several directions. The mantle ultimately consists 
of two layers of tissue—viz., a cortical layer consisting 
of small cells engaged in assimilation, and an inner 
layer of larger cells diminishing in size towards the 
outside. In some cases these larger cells have 
smaller ones intermixed with them. In the forma- 
