i8o 



PHAEOPHYCEAE 



without any mid-rib. A study of the embryonal stages, however, 

 shows that the young plant is flat and bilaterally symmetrical. The 

 two edges then curl up and the plant tears down the centre giving 

 rise to two lateral scrolls each unrolling from a thickened outer 

 margin, but as one of the scrolls soon ceases to develop the mature 

 plant only possesses one scroll borne on a solid bifid stipe with the 

 vestigial scroll on one of the branches. Slitting is represented by 

 rows of small holes which commence to develop after the first tear 

 has taken place. 



Lessoniaceae : Lessonia (after R. P. Lesson). Fig. 121. 



The plants grow erect and form *' forests" in relatively deep 

 waters off the shores bounding the southern Pacific, reminding one 



Fig. 121. Lessonia. A, adult plants of L. fucescens. B, C, seedling stages in 

 L. fucescens. (After Oltmanns.) 



in appearance of some of the fossil vegetation of the Carboniferous, 

 although, of course, there is no connexion. The stipe is extremely 

 stout and rigid, 5-10 ft. long and sometimes as thick as a human 

 thigh. It appears to be more or less regularly branched in a dicho- 

 tomous fashion, a feature which is brought about by the lamina 

 being slit down successively to the intercalary growing region, each 



