1 12 Bristol. — Life-history and Cytology of Chlorochytrium grande. 
wider, and the enclosed spaces are more or less circular, and are very much 
smaller than those towards the centre of the cell. 
In none of the stained preparations, however, was it found possible to 
distinguish any part of the cytoplasm which could be identified as the 
chloroplast as distinct from the rest of the cytoplasm. The position of the 
chlorophyll was therefore determined by cutting sections of the living 
material by means of a freezing microtome. The material was embedded 
in an aqueous solution of gum arabic made as stiff as possible, this substance 
being used to ensure the absence of plasmolysis. The sections were trans- 
ferred at once to a slide, moistened with a drop of water and covered with 
a cover-slip. By these means the preparations were preserved for three 
weeks, because the freezing sterilized the material used, and the drying 
of the gum prevented the ingress of bacteria from the air. When a slide 
was required for experiment the gum was dissolved by adding a little 
water, and the cover-slip could then easily be removed. 
Sections prepared in this way show that the whole of the protoplast, 
with the exception of the nucleus and a thin peripheral film of colourless 
cytoplasm, is saturated with chlorophyll. The surface of the chlorophyll- 
bearing part of the cytoplasm is seen to be raised into numerous small 
rounded lobes (Fig. 9), and it is these lobes that give the characteristic 
mulberry-like appearance to the contents of the living cell. The spaces 
between the lobes are filled with a colourless granular cytoplasm which 
is continued over the whole surface in the form of a thin layer which attaches 
the protoplast to the cell-wall. It is the staining of this surface layer 
of cytoplasm in the permanent preparations which obscures the character- 
istic lobing of the chloroplast and renders its identification uncertain. The 
intensity of staining of the peripheral cytoplasm is identical with that of the 
internal reticulum, hence it may be concluded that the reticulum is also 
composed of strands of colourless cytoplasm containing numerous deeply 
staining granules. 
The internal structure of the cell may thus be described as consisting 
of a wide-meshed cytoplasmic reticulum with a large central nucleus and 
containing a single massive chloroplast which occupies practically the 
whole cell except the nucleus and which is raised into numerous small 
rounded lobes at its surface. 
Sections cut with the freezing microtome show the presence in the 
cytoplasm of a considerable quantity of a bright yellow oil. With osmic 
acid this oil very slowly assumes a deep brown colour, and is then seen to 
exist in the form of globules of very varying sizes (Fig. 10) ; the oil is 
dissolved out of the cell with alcohol. 
The action of iodine upon sections of the living material demon- 
strates the presence of innumerable minute granules of starch scattered 
evenly throughout the cytoplasm. They are so numerous that a section 
