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MALAY FORM OF CHLOROCOCCUM HUMICOLA. 475 
sides of the vessel, but also flat green strata floating about in the liquid. 
Repeated examination has shown that the three cultures are unialgal 
éultures of Chlorococeum humicola (Nig.), Rabenh., and an excellent 
opportunity has thus presented itself of making a study, not only of the life- 
history, but also of the cytology of the alga. 
III. Tug VEGETATIVE CELL. 
The ordinary vegetative cells of the alga are spherical or subspherical, and 
may be either solitary or collected together into small globular clusters or 
into flat expanded strata in which the cells are imbedded in mucus. One 
very important characteristic of the alga is the enormous variation in the 
size of the vegetative cells which make up a stratum. A great many appear 
to be fully grown when they have reached a diameter of less than 20 p, while 
others continue to grow until a diameter of as much as 80, has been 
attained. 
A vegetative cell of diameter about 13 shows a very characteristic 
structure (Pl. 17. figs. 1-4). The wall is thimand is composed of cellulose, and 
it is usually of a uniform thickness throughout, though occasionally one 
or more slight thickenings may be seen (fig. 3). There is a single parietal 
chloroplast, which may take the form of a deep green layer lining practically 
the whole of the cell-wall with a single small colourless area on one side 
(fig. 2), or it may be irregular (fig. 1), having, in some cases, almost the 
appearance of being divided up into several smaller chloroplasts. A large 
pyrenoid is very conspicuous in the chloroplast, and in some cells, particularly 
in the larger ones, two or even as many as half a dozen may be seen, though 
the latter is exceptional. Starch is present in the form of minute granules 
scattered throughout the cytoplasm as well as in the starch-sheaths of the 
pyrenoids. As the cells increase in size, oil is formed and stored in the cells, 
so that their structure cannot be so clearly made out. In the very large 
cells, the chloroplast is usually continuous over the whole surface of the 
cytoplasm with only one, or perhaps two, perforations, and the pyrenoids 
are less conspicuous, the whole contents of the cell being masked by the 
presence of a great quantity of yellow oil and by the frequent development 
of a bright red pigment dissolved in the oil. When a cell has attained its 
full size, the cell-wall, which up to this time has remained quite thin, begins 
to thicken and become stratified, and a number of button-like excrescences 
are formed usually on the inside but occasionally on the outside of the wall. 
But in no case does the wall ever become thicker than about 4, and the 
number of striations is usually few. « 
Stained preparations of the material were made by fixing with Bouin's 
solution and staining with Heidenhain's iron-alum-hematoxylin and with 
Delafield^s haematoxylin. Comparatively little information could be obtained 
