by the Method of Dark-ground I Humiliation. 617 
What is indicated is that the colloid state of the nucleus differs from that of 
the cytoplasm, and that the so-called nuclear membrane represents possibly 
nothing more than the surface which is formed between the hydrosol 
complex of the cytoplasm and the gel structure of the nuclear plasm. 
It is hoped that some further studies of nuclear structure may be 
possible. 
§ 7. The Chloroplast. 
A few observations and notes on the structure and behaviour of the 
chloroplast have been collected, and these indicate rather clearly that this 
structure is to be considered, in cases examined, as rather definitely 
differentiated from the rest of the cytoplasm. 
The chloroplast has usually been observed as slightly opaque and 
heterogeneous, with a motionless gel structure, containing the green pigment 
which is probably in definite solution or absorbed by the gel. Even when 
the cytoplasm is filled with active particles, as in Spirogyra, Elodea y 
Mongeotia , the chloroplast shows a fixed structure. 
The chloroplasts in Elodea moved by the protoplasmic stream do not 
move as rapidly as the stream, indicating that they are rather separated or 
isolated from it. 
Where there is a large chloroplast, as in Spirogyra y it generally behaves 
towards reagents as if it were a structure more or less separate, and differing 
in its attributes. On plasmolysis here, it often remains coiled round the 
outside of the contracted protoplast, and suffers no apparent change in 
organization. Fixing agents, although coagulating the hydrosols and pro- 
ducing a general heterogeneity in the cytoplasm and even the gel of the 
nucleus, do not seem to change the structure of the chloroplast to any marked 
extent. After prolonged action of the agent, and after the colour has been 
removed from the chloroplast, a greater opacity is sometimes apparent. 
The most striking case of distinction was in the action of dilute potash on 
the cell, especially in the plasmolysed state, — the cytoplasm becomes 
extremely white and dispersive of light (PI. XLI, Fig. 4), while the walls 
of the vesicles become almost or quite opaque. This change takes place 
whether the potash is added to the living cell or to the cell after fixation. 
The chloroplast, however, remains quite clear green, and presumably almost 
unaffected by the reagent. It appears as a dull green band, wound round 
the intensely white mass of the rest of the protoplast. No explanation of 
the action of potash on the protoplast to account for this has been found. 
A similar effect is produced by several other reagents, generally of an 
alkaline character — potassium carbonate, ammonia solution, slightly by 
potassium hydrogen carbonate, and so on. 
It seems quite probable that some sort of membrane or bounding 
surface exists between the chloroplast and the cytoplasmic hydrosol, much 
