THE CHLOROPHYLL APPARATUS 145 
plasm of the cell (fig. 85). Even in the lowly forms it is 
apparently never uniformly distributed through the body 
of the protoplast. The form, dimensions, and structure of 
the chloroplast differ considerably in the different groups of 
plants. In some of the filamentous green seaweeds it may 
appear as variously shaped bands or plates. Spirogyra 
shows it as a spiral band passing round the cell; in Zyg- 
nema it has the form of two star-shaped masses which are 
attached to the cytoplasm by bridles ex- 
tending to the cell-wall. In the brown 
and red seaweeds the plastids are not 
green, but have the appropriate colours 
of the plants. These plastids contain 
other pigments in addition to the chloro- 
phyll, but the latter can he made ap- 
parent by-extracting the cells with cold 
distilled water, in which the other pig- Fic. 85—Cutoropuasts 
ments are soluble. In all plants higher in PXPPPDPD IN GE PRO. 
TOPLASM OF A CELL OF 
the scale than the Alge the chloroplasts T™®, PAutssve Tissun 
or a Lumar, 
are found as round or oval bodies em- 
bedded in the cytoplasm. They never occur in the vacuoles 
of the cells. Though normally green, they can assume 
other colours, such as yellow, brown, or red, but this is due 
to an alteration of the pigment they contain. Examples 
of this change are afforded by the assumption of the 
autumnal tints by foliage leaves, and by the changes in 
colour which are characteristic of ripening fruits. 
In the Mosses the chloroplasts are found throughout 
the cells of the leaves, in the outer parts of. the sporo- 
gonium, and in certain cells of the axis. In the Ferns they 
occur chiefly in the leaves, occupying the cells of the 
epidermis as well as those of the mesophyll. In the 
higher plants they are found most prominently in the 
mesophyll of the leaves, the epidermis as a rule being free 
from them. When the leaves are dorsiventral in structure, 
the chloroplasts are more numerous in the palisade paren- 
chyma which lies just below the upper epidermis than they 
10 
