Carter. — Studies on the Chloroplasts of Desmids. III. 269 
The species of Cosmarium examined during this investigation included 
C. subtumidinn , Nordst., C. punctidatum , Breb., C. contr actum, Kirchn., 
C. crenatum , Ralfs, C. depressum , Lund., C. caelatum , Ralfs, C. speciosum , 
Lund., ( 7 . cucurbit a, Breb., ( 7 . curium, (Breb.) Ralfs, C. elegantissimum , 
Lund., C. diplosporum, (Lund.) Lutkem., C. pyramidatum, Breb., C. pseudo - 
pyramidatum , Lund., C. achondroides , West, C. pseudoconnatum , Nordst., 
( 7 . ornatum , Ralfs, ( 7 . Ralfsii , Breb., ( 7 . praemorsum, Breb., ( 7 . formosidum , 
Hoff, ( 7 . binum , Nordst., ( 7 . margaritiferum, Menegh., ( 7 . Turpinii , Breb., 
( 7 . pachydermum , Lund., ( 7 . ochthodes, Nordst., ( 7 . Botrytis , Menegh., C. 
tetraophthalmum , Breb., ( 7 . amoenum , Breb., ( 7 . subcucumis , Schmidle, ( 7 . 
reniforme , (Ralfs) Arch., ( 7 . biretum , Breb., ( 7 . Brebissonii , Menegh., 
( 7 . cucumis , Corda, 6". controversially West, ( 7 . ovale, Ralfs, and ( 7 . Askenasyi , 
Schmidle. Of these thirty-five species the first thirty have axile chloroplasts, 
of which twelve have one point of pyrenoid formation per semi-cell, thirteen, 
two points of pyrenoid formation, whilst in five the chloroplast has an 
unusual structure. The five last-mentioned species have parietal chloro- 
plasts. 
All the species examined having axile chloroplasts have either one or 
two chloroplasts in each semi-cell. When only one is present it occupies 
a central position, whilst when there are two they are placed transversely, 
side by side in the semi-cell. The pyrenoids are usually, though not 
invariably, embedded in the axis of the chloroplast, often typically one in 
each, which may give rise to a group of two to four. In a few species more 
pyrenoids than one are invariably present in each chloroplast, in which case 
the latter is always unusual in shape. With the exception of C. Ralfsii the 
points at which pyrenoids may occur are nearly always definite and fixed. 
The axis of the chloroplast containing the pyrenoids is always provided 
with a variable number of strands or more definite plates which radiate 
towards the cell-wall. Their peripheral edges sometimes spread out over 
the latter, forming more or less extensive parietal layers or films of chloro- 
plast. In a few species these parietal films are the seat of numbers of small 
proteid granules or naked pyrenoids (Figs. 37-49, 56, and 70). The latter 
have no relations with the large pyrenoids in the axis of the chloroplast, and 
are probably formed de novo when the conditions are favourable. 
C. subtumidinn , C. punctidatum , C. contractum , C. crenatum , 
and C. depressum . 
The simplest chloroplasts of the genus were found in these five species, 
and here, corresponding to the shape of the semi-cell, there is a rather 
massive axis in the centre, containing usually one pyrenoid (Figs. 3-5, 7, 9, 
18-20, and 32). If this original pyrenoid divides, the products of its 
division may sometimes separate to some little distance, because of the 
comparatively great width of the axis (Fig. 2), but. although they may not 
