KONGL. SV. VET. AKADEMIENS. HANDLINGAK. BAND. 20. N:0 5. 181 



of Antithanmion found in the White Sea to differ in certain points from the typical A. 

 plumula, and on this account he sets it down as a variety of this, by the name of var. 

 boreale. He further elucidates Callitham^ion lajiponicum, which Ruprecht has first de- 

 scribed, though scarcely in such a manner as to make it possible to recognize it. This 

 form Gobi regards as intermediate between A. plumula f. typica and f. boreale. At the 

 same time, pointing out that A. plumula is closely allied to A. (Callithamnion) ameri- 

 canum, he utters the supposition that the latter alga is to be regarded only as a form 

 of the former. Gobi ends his disquisition with the following words: »Es ist bekannt, 

 dass A. plumula eigentlich dem Gebiete des Atlantischen Oceans und des Mittelmeeres 

 angehort; im nordlichen Ocean kommt diese Form schon viel seltener vor und zwar 

 vereinzelt in sehr diinnen Btischeln von unbedeutender Grosse . . . Folglich erscheint sie 

 fur den nOrdlichen Ocean nicht als eine aborigene Stammform, sondern vielmehr als 

 eine dahin eingewanderte und dabei sehr stark veranderte.» 



I quite agree with Gobi in thinking A. ainericanum to be nearly related to A. 

 plumula, especially to A. plumula var. boreale Gobi. But if the former alga should not 

 be regarded as a distinct species, a great many other Antithamnia described as inde- 

 pendent species would on perhaps as good grounds have to subsumed as various forms 

 under the same species. There are to be found transitions between A. americanum and 

 A. Pylaisoei according to Farlow (New Engl. Alg. p. 123), and A. plumula var. boreale 

 not seldom shows a strong tendency towards the latter species. C. corallina Rupr., 

 which is connected by intermediate forms with A. plumula var. boreale, is plainly very 

 closely allied to A. cruciatum, so that it might with as great reason be considered as 

 a form of this species as of A. plumula or A. americanum. To this may be added 

 that the distance between A. Pylaisoei, especially the form occurring on the coast of 

 Norway, and A. floccosum is not great. In specimens of A. Pylaisoei from Finmarken 

 I have seen branch-systems of the last order replaced here and there in the frond by 

 simple subulate branches of the shape characteristic of A. floccosum, which makes me 

 think that these two plant, considered hitherto as species, are connected by intermediate 

 forms. Thus, if A. americanum he reduced, the reduction ought apparently to be ex- 

 tended to several other species. I am of opinion that the genus Antithamnion is a young 

 genus whose species are in course of development, no marked differentiation being as 

 yes established and the transitional forms not having disappeared. If the common prac- 

 tice with regard to such genera, Salix, Rubus a. o., is to be followed, according to 

 which every form met with in greater quantity at different places and easy of re- 

 cognition is considered as a species, both Antithamnion plumula var. boreale Gobi, com- 

 monly distributed in the Polar Sea, and A. plumula, A. americanum, A. Pylaisoei, A. 

 floccosum and A. cruciatum ought to be regarded as distinct species. It is by these con- 

 siderations that I have been led to set down the polar form as an independent species: 

 A. boreale Gobi. On the other side, I cannot but hold, with Gobi, Callithamnion lapponicum 

 RuPE. and also C. corallina Rupr. to be forms of A. boreale, as these certainly do not 

 differ so much from A. boreale, as this does from A. plumula and other Antithamnia. 



A. boreale differs from A. plumula by the different branching, by longer cells 

 in the main axis and in the long branches of the frond, and by its sessile tetra- 



