378 



IV. Cyanophyceae 



(determined by Johs. Schmidt). 



Fam. Chamaesiphonaceae. 



Pleiirocapsa ainethystea Rosenv. Gil. Havalg. p. 967 var. 



An epiphyte ^) on Rhodochorton Rothii. In shape and size the Ice- 

 landic specimens hardly differ from the Greenlandic, of which 1 have had 

 opportunity to see some of the author's original preparations. The large 

 cells, in which cell-divisions have not yet begun, are roundish, isodia- 

 metrical or somewhat depressed. The divisions of the mother cell begin 

 with vertical walls in different directions, and thus the plant increases 

 horizontally and takes a shape of a low crust. Afterwards as the hori- 

 zontal walls appear, it becomes composed of many layers and its thickness 

 increases. The cell-colony, which is formed by divisions of the single 

 mother-cell, becomes ultimately an approximately semiglobular cluster of 

 angular or rounded cells. These cell-colonies often attain a considerable 

 thickness, and as they often are much expanded horizontally, they join 

 other cell-colonies, which are developed from other mother cells; in this 

 manner the large Pleurocapsa-mantles are formed, which surround the 

 filament of Rhodochorton Rothii and often attain a far greater thickness 

 than the filament of the host. 



How the spores escape, I cannot see in my preparations. 



The shape, size and the progress of the ceU-divisons seem, as men- 

 tioned above, to be the same in the Icelandic and Greenlandic plants-), 

 but the colour of the content of the cells is different. Kolderup Rosen- 

 vinge describes the colour of the Greenlandic plants as „sordide violacea". 



1) Lagerheim (Mykologische Studien, III Beitr. zur Kenntniss d. parasitischen 

 Bacteiien und der bacterioiden Pilze, Bih. till K. Sv. Vet.-Akad. Handlingar 

 Bd. 26, Afd. Ill, Nr. 4, 1900, p. 3— 15) describes from Drobak in the Kristiania 

 f^iord a similar organism, Sarcinastrum Urospora} Lghm., which is colourless 

 and taken for a bacterium, but I think it rather ought to be regarded as 

 a colourless, parasitical or saprophytical Pleurocapsa-species. It grows in 

 the walls of Urospora mirabilis Aresch. and causes gall-like swellings in the 

 cells of the host plant (cfr. 1. c. Tab. f, 1—6). Regarding the Icelandic and 

 Greenlandic specimens of Pleurocapsa amethystea nothing of that sort is 

 the case; they grow on the surface of the host and the cellwalls of tlie 

 epiphyte and the hostplant are distinctly separated ; at the most there may 

 be seen a deepening in the walls of the hostplant where the epiphyte 

 grows. 



2) Such regular divisions, as figured by Kolderup Rosenvinge (1. c. Fig. 57, E). 

 1 have never seen. 



