Acton . — Observations on the Cytology of the Chroococcaceae . 445 
whole wall is soluble in caustic potash solution. On testing with picro- 
sulphuric acid the thin darker layers take on a yellow tinge, showing the 
presence of chitin. No colour reactions for cellulose could be obtained. 
Generalizations as to the nature of the cell -wall in the Cyanophyceae 
seem to have been derived from studies of filamentous form only. Hegler 
(’01) states that the sheath is chitinous, the gelatinous coat pectose in nature. 
Kohl (’ 03 ) observes that in the Cyanophyceae the membrane and sheath 
consist largely of chitin with some cellulose, the gelatinous sheath of pectose. 
The amount of cellulose present is often not sufficient to give the usual 
colour reactions. Speaking of Tolypothrix , he says, p. 92, ‘ ... in der Scheide 
das Chitin, in der Membran der Cellulose pravaliert ’. Massart (’ 02 ) says 
the walls are not of cellulose, and a gelatinous sheath is often present. 
These observations cannot include forms like Chroococcus macrococcus , in 
which the envelope consists of alternating layers of pectose and chitin. 
The irregular splitting away of the outer coats is probably due to the 
fact that the chitinous layers are incapable of rapid expansion, while the 
pectose layers swell with ease. The ecdysis of the older layers is always 
more noticeable in cells which are actively dividing after a period of rest. 
Culture experiments were made to ascertain the effect of various media 
on the development of the cell-wall. It was found that solid media pro- 
duced a one-sided development of the cell-wall. Cultures on damp earth 
showed, in three weeks, a considerable increase in size of the cell-wall on 
the side nearest the earth (Fig. 22). This was shown also in agar cultures, 
but not to the same extent, development being much slower. 
The most striking results were obtained by removing material which 
had been for eighteen months on an agar culture to a 2 per cent. KN 0 3 
solution. The cell-wall elongated rapidly on one side, and, as the cells 
divided, corrugated stalks were formed (Fig. 23). 
(b) Protoplast . 
In the living condition the protoplast is too densely coloured to show 
much structure. Often it is not evenly coloured in all parts, and so an 
appearance simulating a star-shaped chromatophore arises. Cells which 
are golden brown in colour are frequently crowded with large refractive 
globules. These appear to be yellow, but whether they contain pigment or 
not has not been determined. They are not soluble in alcohol and do not 
blacken with osmic acid. One or more blood-red pigment spots can also 
be seen. 
The pigment is not easily dissolved out of the cells, so all the earlier 
preparations were cleared in a 2 per cent, solution of KOH before staining. 
There was too much shrinkage in these preparations for detailed investiga- 
tion, but they were useful in showing that a portion of the protoplast is 
definitely marked off from the remainder by its staining properties, having 
H h 2 
