PORPHYRIDIUM CRUENTUM NAEGELI 
337 
27). The pyrenoid is generally spheroidal in shape, though when the cell 
starts to divide it lengthens and becomes somewhat angular. As a rule it 
stains uniformly dark, though at times it appears ring-shaped with a rela- 
tively unstained center (figs. 25-27). 
A single eccentrically located globule, a trifle smaller than the pyrenoid, 
has been frequently noted in Porphyridium. It can be seen very easily in 
the living specimen and has been observed to fragment as the water content 
of the cell increases, the fragments arranging themselves about the chromato- 
phore. Except in its reaction toward acid carmin it seems to act as if it 
were cyanophycin. In general, we find, it takes the usual nuclear stains, 
haematoxylin, gentian violet, and safranin. 
Picric acid has, on the whole, given the best results as a fixing fluid. 
If it is washed out in running water, the chromatophore will be dissolved 
and the pyrenoid and ''nucleus" left without being obscured by any other 
cell structure. Ten minutes in the acid is enough for the fixation, and from 
fifteen minutes to twelve hours will do for the washing out of the fixative. 
Mordanting for one hour in iron alum and staining for a like period in 
haematoxylin have given the best results with this stain. Staining for 
ten minutes over a water bath is sufficient for anilin-gentian violet and 
anilin-safranin, and the specimen can then be decolorized by allowing it 
to stand over night in methyl alcohol. Another very successful fixative and 
mordant is: 
Pyrogallic acid (25 % aqueous sol.) 10 parts 
Ferrous sulphate (sat. sol.) 5 parts 
Fuchsin (sat .ale. sol.) i part 
Van Ermengen's osmic acid process has given only fair results. When- 
ever the material was fixed in either of Flemming's fluids, or when fixed in 
picric acid and hardened in alcohol, the chromatophore stained so densely 
that it was impossible to distinguish anything in the cells clearly. Flem- 
ming's triple stain has given very fair results. 
The chromatin, consisting of a single eccentric granule surrounded by a 
clear space in the cell (fig. 18), is typical of the resting stage, a stage described 
by Brand as "wasserarm." The cell, however, if dried, is useless as far 
as any clear results are concerned. As the cell prepares for division, this 
granule enlarges and begins to fragment, assuming the various shapes shown 
in figures 18-27. No hard and fast rule can be laid down for establishing 
a sequence of forms in this breaking up, as there are many forms which do 
not fit well into any series that could be arranged out of the others, although 
some of the shapes occur in many cells. The "U" shape is perhaps the 
most common (figs. 21, 22), and it is not at all unusual to find the fragments 
united in a line (figs. 23, 24) or in a ring (fig. 20). Frequently the pieces 
in drawing apart leave trails which have a striking resemblance to the 
mitotic spindle (fig. 25), which resemblance seems to be purely accidental. 
As an end result of this fragmentation the chromatin is distributed in the 
