Algal Ancestry of the Higher Plants. 247 
are merely diverging developments from a common ancestral 
sporogenetic and gametogenetic thallus. 
Such a view is, moreover, quite in accord with the hypothesis 
put forward above in connection with the origin of the two 
generations of the Pteridophyta from a Chaetophoraceous ancestry, 
and we have here a good illustration of how diverse the two 
diverging generations may soon become. It is interesting to note 
that the morphological origin of the two generations in Cutleria is 
just the reverse of that postulated in the Clnetophorales, the 
sporophyte being prostrate, the gametophyte erect, a variation only 
too likely to occur in groups where alternation was in the making. 
Finally, we may briefly consider the alternation that has been 
observed in the Red Algae. In this group also, differentiation of 
the thallus into a creeping basal portion and an upright system is 
frequently observed, especially in the simpler forms (e.g., Batvacho- 
spermum, Chantransia), but in the vast majority it is the upright 
system that has been elaborated, with more or less complete 
elimination of the basal portion. Two types of alternation are 
known in the Red Algae, viz., the type characteristic of Nemalion 
and presumably of many of its immediate allies, and the complex 
alternation typical of the more advanced forms. 
The case of Nemalion is very similar to that of Coleochcete, the 
sporophyte (as constituted by the sporogenous threads forming 
carpospores) appearing as an intercalated stage. Wolfe' came to 
the conclusion that reduction occurred at the end of this intercalated 
phase, viz., on the formation of the carpospores. Svedelius 2 has, 
however, recently investigated Scinaia fuvcellata, another member 
of the Nemalionales, and finds that the oospore undergoes reduction- 
division at the inception of germination, three of the four nuclei 
produced aborting, whilst the remaining one is used in the formation 
of the sporogenous threads. It seems probable that this is the 
usual course of events among the Nemalionales, which therefore, as 
regards their life-cycle, are in almost complete agreement with 
Coleochcete. Presumably matters are the same in Batvachospermum ; 
here, however, the carpospores, on germination, give rise to the 
well-known Chantransia-stage, that is a mainly prostrate system of 
creeping threads, from which the Batrachosper //mw-plant arises as a 
side-branch. This sequence is very similar to that occuring in 
Mosses, and here we have the state of affairs postulated on p. 12. 
1 Annals of Botany, XVIII, 1904, p. 608. 
3 Nov. Act. Reg. Soc. Seient. Upsala, ser. IV, Vol. IV, No. 4, 1915. 
