150 VEGETABLE PHYSIOLOGY 
to lecithin. He held it to be an ester of an unsaturated 
alcohol to which he gave the name phytol (Cop HywO). 
Except in the lowest unicellular plants, the chlorophyll is 
always attached to some form of protoplasmic body or 
plastid. These are small masses, of varying size and shape, 
which are embedded in the general cytoplasm of the 
cell (fig. 85). Even in the lowliest plants it is apparently 
never uniformly distributed through the body of the proto- 
plast. The form, dimensions, and structure of the chloro- 
plast 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 Zygnema it has 
the form of two star-shaped masses which are attached 
to the cytoplasm by bridles extending 
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 chlorophyll, 
but the latter can be made apparent 
by extracting the cells with cold dis- 
tilled water, in which the other pigments 
Fra, 86.—Cutororrasts aye goluble. In all plants higher in the 
EMBEDDED IN THE PRo- 
mortasM or a Cert or Scale than the Alge the chloroplasts are 
Tur PatsapE Tissue found as round or oval bodies embedded 
or A Lear, z 
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 sporogonium, 
and in certain cells of the axis. In the Ferns they occur 
chiefly in the leaves, occupying the cells of the epidermis as 
