Oct. wis.] k, OKAMURA.— UNDARIA AND ITS SPECIES. 277 



var. distans represent the two extreme forms. Prof. Yexdo says 

 " For instance Hirome undarioides Yendo, stands as an inter- 

 mediate form between Undaria pinnatifida Sur., and Laminaria 

 radicosa KjELLM., in its habit, texture and propagating or- 

 gans,"^ To me that species seems to stand as an intermediate 

 form between Undaria pinnatifida and U. Peterseniana. 



It will be natural to think that man}' plants among Lami- 

 nariaceas have descended from a certain ancestral form or forms. 

 What the ancestral form was is unknown to us, but considering 

 the facts about ontogeny of Laminarian plants it is probable 

 that a Laminarian form is ancestral. Now, Undaria Petersen- 

 iana is more primitive in the form of frond and soriferous area 

 than U. pinnatifida. The hitherto monotypic genus, Undaria, 

 stands isolated on account of its highly specialised form. If we 

 take U. Peterseniana as the original form we can easily trace 

 the phylogeny of U. pinnatifida, otherwise difficult. The undu- 

 lato-plicating of the basal part of soriferous frond of Undaria 

 Peterseniana in continuation with the upper portion of the wing 

 rnay be considered as indicating the beginning of sporophylls. 

 Through U. undarioides and U. pinnatifida f. typica the wing 

 might have developed to well-defined sporophylls of f. distans. 

 The continuation of sori from the base of lamina to the sporo- 

 phylls in f. typica may be considered as a retroversion of sorus 

 passed from the lamina to sporophylls. It is a well known fact 

 that an aberrant form of any plant often reveals its phylo- 

 genetical characters. It would appear a.t a glance absurd that 

 while the original form has a narrower range of distribution, 

 the derivative a wider ; yet a parallel can be seen in gymno- 

 sperms and angiosperms. 



Of the affinity of Laminaria Peterseniana Kjellm. the author 

 of that species says " L. Peterseniana hat gefliigelten Stipes uud 

 Sori auf der Lamina und ist gewissermassen eine Zwischenform 

 zwischen dem reinen Laminaria-Typus und dem Saccorhiza-Ty pus. 

 Letzterer stand bisher isoliert durch das Vorkommen der Zoospo- 



1) Yendo : The Devel. of Costaria, Undaria and Laminaria (Ann. of But. Vol. 

 XXV, 1911) p. 691. 



