186 



Tetrasporineae 



B 



Fig. 112. Coccomyxa subellipsoidea Acton, 

 x 1000. The dotted lines indicate the 

 extent of the colourless mucus surrounding 

 the cells. 



It seems probable that the, genus EcbaUocystis is rightly placed in this group as the 

 colonies are fixed by mucilaginous stalks which are mostly concrescent. The division of 

 the ellipsoidal cells is also obliquely longitudinal (vide Bohlin, '97, t. 1, figs. 3 and 4). 



Sub-family PALMELLE^K. The Alga? of this small sub-family consist of 



aggregates of globose or ellipsoid cells 

 irregularly grouped within a structure- 

 less mass of mucus. The latter is usually 

 of indefinite extent, as in Palmella, but 

 in Palmodactylon it is more or less 

 cylindrical and often much branched, 

 while in Sphserocystis it is mostly glo- 

 bose. In some of the genera (Palmella, 

 Coccomyxa, Sphasrocystis) reproduction 

 occurs by biciliated zoogonidia, and in 

 Palmella, by isoplanogametes ; but in 

 others (Palmodactylon) the cells mul- 

 tiply only by division, which may be 

 in any direction of space. In Cocco- 

 myxa the division-planes are mostly 

 oblique and there is a sliding growth 

 of the daughter-cells (fig. 112 C and D). 

 The chloroplast is a parietal plate or cushion, of variable form, and with or 

 without a pyrenoid, and on its inner side, sometimes within a hollow, the 

 nucleus is situated. 



The genera are : Palmella Lyngbye, 1819 ; em. Chodat, 1902 ; Palmodactylon Nageli, 

 1849; Sphtvrocysti* Chodat, 1897 ! ; Pseudotetraspora Wille, 1896; Coccomyxa Schmidle, 

 1901. 



All the genera are freshwater with the exception of Pseudotetraspora, which occurs in 

 the sea oft' the Norwegian coast. Coccomyxa is generally subaerial, and Spheerocystis a 

 frequent constituent of the freshwater plankton. 



Evidence has been brought forward (G. S. W. '09) in support of the view that the 

 plankton-Alga Tetraspora lacustris Lemm. is merely a stage in the life-history of 

 Sphivrocystis Schroeteri Chodat ; and this view receives further support from the fact that 

 pseudocilia have not been demonstrated in Tetraspora lacustris. On the other hand, both 

 forms occurred simultaneously in equal abundance in the plankton of Loch Lomond 

 (W. & G. S. W., '12), an observation which is rather confirmatory of Wesen berg- Lund's 

 statements ('04) that the two are probably distinct. 



1 Wille ('03) has endeavoured to show that Sphserocysti* (Chodat, 1902) should be regarded 

 as synonymous with Glceococcus (A. Braun, 1851), but Chodat ('04) has rightly contested this 

 suggestion. The microscopic limnetic colonies of Splmrocystis have nothing whatever in 

 common with Braun's description of the macroscopic colonies of Glceococcus, which must be 

 placed in the category of genera dubia. Wille's reference of the genus to the Chlamydomonadeae 

 (Wille, '03 ; '09) is also erroneous since the dominant vegetative phase is non-motile, and the 

 experience of the present author is that a motile phase may be absent for very numerous 

 generations. 



