LAMINARIALES (HETEROGENERATAE) 173 



from it in that there are no crampons but only a basal attachment 



disk. 



Morphologically both lamina and stipe in Laminaria can be 

 divided into three regions (cf. fig. 116), the outer cortex, the 

 medulla, and the pith or central portion of the medulla. The one- 

 layered blade first becomes two-layered and then the primary 

 tubes of the medulla are cut off and separate the two outside layers. 



Fig. 117. Laminaria. A-F, stages in development of female gametophyte from 

 a spore (A-D x 1333, E-F x6oo). G, male gametophyte ( x 533). H, I, first 

 two stages in development of young sporophyte. J, sporangia {s), paraphyses {p) 

 and mucilage caps (c). (A-I, after Kylin; J, after Oltmanns.) 



Next the cortical cells arise from the cells of the limiting layer by 

 divisions parallel to the surface. Somewhat later the cells of the 

 inner cortex elongate, the middle layer of the common wall be- 

 comes swollen and the cells separate from each other except at a 

 few points where the connexions become drawn out into short 

 secondary tubes. Subsequent increase in thickness is due to growth 

 in the limiting layer and the production of tubes and hyphae 

 together with a considerable development of mucilage, so that the 

 central cells become even more separated from each other. Two 



