411 



Having examined a great number of specimens, partly living plants, 

 from very different localities, I have found it necessary to unite Gomont's 

 two species into one under the name of Phormidium autumnale (Ag.) 

 Gomont emend. 1 ) The extreme forms described and drawn by 

 Gom ont (1. c, p. 184—190, pl. 5, figg. 21 — 24) are generally found in the 

 very same sample in connection with transition forms of each successive 

 stage, and it is not correct, when Gomont (1. c, p. 186) says, that forms 

 with most easely perceptible uncinated apex have the most robust tri- 

 chomatas, for those characters do not always go together. Nor is it 

 possible to distinguish the species biologically by reason of the diffe- 

 rences between their localities 2 ) , for several specimens from quick- 

 flowing waters had the apex nearly straight, while again others, taken 

 from damp earth, often had the apex particularly uncinated or even 

 sinous. Hence I think it impossible to uphold Gomont's two species, 

 but at the same time I should say that the value of Gomonts admirably 

 exact descriptions and drawings must not be underrated. 



43. Oscillatoria Agardhii Gomont. 



Monographie des Oscillariées, II, p. 205, 1892. 



According to P. Richter (Hedwigia, 35, 1896, p. 263 ff. ) this 

 species is identical with sterile specimens without heterocysts of Aphani- 

 zomenon Fios-aquae, where the trichomatas are not as usual connected 

 together in isolated and characteristically formed flakes. It seems to me, 

 that Richters view is wrong. By one of Gomont's authentic specimens 

 from herb. Agardh most kindly placed at my service by Dr. 0. Nord- 

 stedt, I have convinced myself of the independence of this species and 

 its diversity from Apha,nizomenon Flos-aquae, the trichomatas of which 

 never have the peculiar, in Oscillatoria Agardhii well characterized 

 calyptras, by which many homocysteous species are distinguished, while 

 they are never to be found in the other (heterocysteous) families of 

 Gyanophyceae. 



Richter says (I.e., p. 273) that the calyptras on the whole 

 are of no systematic value, because, as he means, they occur too rarely 

 on the species where they have been found and described by Gomont, 

 to be regarded as normal organs. This, I am sure, is not the case, 

 and no doubt Gomont is right; certainly, now and then one will have 

 to examine several trichomatas without finding typically developed calyp- 

 tras; but then the trichomatas are either too young or their apex is 



y ) In Hofman-Bang's herbarium I have examined an original-specimen 

 with Agardh's writing: Oscillatoria autumnalis. It contained tri- 

 chomatas with easily perceptible uncinated apex, and especially 

 others that were nearly straight. The native place of the plant 

 was not given by Agardh. 



2 ) See Gomont himself: „Les Phormdium subfuscum, uncinatum et 

 autumnale se trouvent très fréquemment mélangés entre eux aussi 

 bien qu'avec les Phormidium Corium et papyraceum." 



