Chapter vii 

 THE GREEN PLANT CELL 



Chloroplasts and Chlorophyll. — The majority of 

 plants we are familiar with have green stems and 

 leaves, or green leaves alone. The green colour is 

 due to the mixed pigment chlorophyll present in the 

 chloroplasts (which are definite, oval, spherical or disc 

 shaped, protoplasmic bodies lying in the cytoplasm of 

 certain of the hving cells of the leaf or stem)^ and in 

 these alone. The lower green plants (for instance the 

 Mosses and Liverworts) possess chloroplasts of the 

 same nature as those of the seed plants, but in the 

 Green Algae the chloroplasts are very various in shape 

 and size (e.g. spiral bands. Fig. 9). The chloroplasts are 

 derived from the plastids (which multiply by simple 

 division) found in the meristematic cells, and are not 

 formed afresh in the protoplasm. 



Chlorophyll is a mixture of four different pigments 

 held in the protoplasm of the chloroplast in a colloid 

 state : chlorophyll a (C55H7205N4Mg) giving a blue- 

 green solution, chlorophyll )3 (CjjHyoOjN^Mg) giving 

 a pure green solution, carotin ' (C^o^se) giving orange 

 crystals, and xanthophyll (C^o-^se^a) giving yellow 

 crystals. These are mixed in the chloroplasts in the 

 proportion of six molecules of the two green pigments 

 to two of the two orange and yellow ones. 



' Carotin also occurs in other parts of various plants. It is, for 

 instance, the red colouring matter of carrots, of many red and orange 

 coloured flowers, etc. ; also of the " eyespot " in Chlamydomonas 

 (see p. 186). 



112 



