i82 PHAEOPHYCEAE 



laminae that bear sporangia in longitudinal folds when they are 

 mature. Apart from the cryptostomata of Saccorhiza and Alaria it 

 has also been suggested that the occurrence of these sporangia m 

 folds may illustrate how the fertile fucalean conceptacle may have 

 arisen. Such a change would necessitate the development of wedges 

 of sterile tissue in order to divide up the folds, but whether such a 

 change could occur in a relatively differentiated thallus is a matter 

 for speculation. 



The numerous laminae are formed by a splitting process in 

 which a portion of the lamina fails to continue growth whilst the 

 rest goes on growing, and in this manner a weak area is formed 

 from which a split commences. 



Lessoniaceae : Nereocystis {Nereo, Nereis, daughter of Nereus; 

 cystis, bladder). Fig. 123. 



The plants, which from the recorded observations appear to be 

 annuals, may attain a maximum length of 90 m. bearing a bladder 

 up to 2 or 3 m. in length. The long slender stipe is solid and cylin- 

 drical below but swollen and hollow above, finally contracting just 

 below the terminal spherical bladder which bears a row of short 

 dichotomous branches, each giving rise to a number of long thin 

 laminae. The plant commences with only one blade which divides 

 twice in a dichotomous fashion, thus producing four blades, and 

 these form the centre of activity for the remainder through a 

 process of shtting. The splitting of these four fronds is preceded by 

 the development of a distinct line along the path of the future slit, 

 the line representing new tissue, which has in consequence very 

 little strength, thus forming an area of weakness along which the 

 slit commences. The plant is found at a depth of from 5 to 25 m. 

 between Alaska and Los Angeles. Besides being a good source of 

 potash salts, as the ash contains 27-35 % potassium chloride, the 

 stalk and vesicle can be treated to yield a candied edible product 

 called " Seatron". Locally it is called by a number of names, bull 

 kelp, bladder kelp, ribbon kelp and sea-otter's cabbage. 



In the closely related genus Pelagophycus the spores are said to 

 be non-motile, not even possessing cilia. Further confirmation of 

 this fact is much to be desired because not only is it an unique state 

 in the family but it also renders comparison with Nematophyton (cf. 



