150 VEGETABLE PHYSIOLOGY 



to lecithin. He held it to be an ester of an unsaturated 

 alcohol to which he gave the name phytol (C 20 H 40 0). 



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 

 FIG. 85.-CHLOROPLASTS are soluble. In all plants higher in the 



EMBEDDED IN THE PfiO- - *, . 



TOPLASM OF A CELL OP scale than the Algae the chloroplasts are 



THE PALISADE TISSUE found as round or oval bodies embedded 



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 



