Fig. 99 Laminaria. A-F, stages in development of female game- 



tophyte from a spore (A-D x 1333, E-F x 600). G, male game- 



tophyte ( X 533). Hj I, first two stages in development of young 



sporophyte. J, sporangia (5), paraphyses {p) and mucilage caps (c). 



(A-Ij after Kylinj J, after Oltmanns.) 



would seem to fulfil this requirement. In some species many of the 

 other cells also contain pits with a thin membrane across the open- 

 ing and these presumably facihtate the diffusion of food materials. 



Most of the genera possess systems of anastomosing mucilage 

 ducts. In L. cloustoni these are confined to the stipe and in L. 

 digitata (and Nereocystis) to the frond, but in L, saccharina they 

 occur in both organs. In the genus Egregia they are absent. When 

 mature there are periodic openings from these ducts to the exterior 

 and their bases are lined with secretory cells. They arise lysigen- 

 ously through an internal splitting of the thallus due to cell disin- 

 tegration : this is followed by a differential growth so that the canals 

 become more and more submerged in the thallus. The attachment 

 organs or crampons, which are positively geotropic, have an apical 

 growth and differ from the rest of the thallus in that there are no 

 connecting hyphae nor is there any pith. The amount of conduction 

 necessary in these plants would be expected to be small, but even so 



177 



