140 



PHAEOPHYCEAE 



There is also a certain amount of secondary tissue which in some 

 parts may be rhizoidal in character. 



In Mesogloia there is a single central strand terminating in a hair 

 and having a distinct intercalary meristem just below the apex. 



L.T.4^ 



P.A. 



C.HA 



CORTEX- 



Fig. 94. Mesogloia veryniculata. A, plant (sporophyte). B, apex of filament with 

 branches and beginning of cortication ( x 135). C, unilocular sporangia. D, pluri- 

 locular gametangia on gametophyte. E, diagram to illustrate construction of 

 thallus (central thread type). C.i/. = colourless hair, L.T.= leading thread with 

 intercalary growth zone, P.y3.= primary assimilator, 5".^. = secondary assimi- 

 lator, »S.c. = secondar>^ cortex, 6'.5C. «= secondary' sub-cortex. F, diagram to 

 illustrate life cycle. (A, C, D, after Tilden; B, E, F, after Parke.) 



The cortex is formed of short horizontal filaments with somewhat 

 globose terminal cells that are packed in a gelatinous material. 

 The hairs, which are frequently worn away in the older parts of the 

 thallus, occupy a lateral position, but owing to inequahties of 



