EUPHYCOPHYTA 



171 



There are four families in the order : 



(a) Chordaceae : this is monotypic. 



(b) Laminariaceae : the species either possess a simple blade or 

 one that is segmented longitudinally, but the spHts do not 

 extend into the transition zone so that there is only one 

 intercalary meristem. 



(c) Lessoniaceae : the spUts of the primary blade extend into the 

 transition zone so that each segment has a stalk and an inter- 

 calary meristem. 



(d) Alariaceae : these have special lateral sporophylls. 



Chordaceae : Chorda (a string). Fig. 96 



The long whip-like thallus, which is clothed in summer with 

 mucilage hairs, arises from a small basal disc with the growing 

 region situated just above the holdfast. The hollow fronds are 

 simple with diaphragms at intervals, the construction of the thallus 

 being essentially that of a multiseptate cable derived from the 



Fig. 96 Chorda filum. A, plant ( x |). B, transverse section, high- 

 power, with sporangia. C, female gametophyte ( x 145). D, male 

 gametophyte ( x 175). (A, original; B, after Oltmanns; C, D, after 



Kylin.) 



