CHROMATOPHORES 



37 



Chromoplasts are coloured yellow, orange, or red by various pig- 

 ments, which are probably all closely related as regards their chemical 

 constitution. In some cases the characteristic pigment is suspended 

 in a colourless protoplasmic matrix [or stroma] in an amorphous state, 

 or rather in the shape of minute globules or vesicles (grana) ; in others 

 it takes the form of crystals, which may be tabular or rod-shaped, but 

 which most often are exceedingly slender and irregular spindle- or 

 needle-shaped bodies scattered through the matrix or collected into 

 bundles or sheaves (Fig. 4 b). Occasionally more than one kind of 

 colouring matter is present in the same chromoplast. The chromo- 

 plasts of the mesocarp of Lycopersicum escnlentum (the Tomato) and of 

 Solarium dulcamara, for example, contain both yellow grana and red 

 crystals. In certain cases the crystalline pigment is accompanied by 



Fig. 4. 



A. Cell from a perianth-segment of Hemerocallis fulva, showing spindle-shaped 

 chromoplasts. B. Chromoplasts from fruit of Sorbus. Avcuparia, filled with a 

 dense weft of thread-like crystals of colouring matter. C. Lobate chromoplasts from 

 the petals of Genista tinctoria. A and B after Schimper. 



protein-crystals (crystalloids). Chromoplasts may be spherical, spindle- 

 shaped, or quite irregular in outline (Fig. 4) ; their form is very often 

 modified or altogether determined by the crystalline inclusions. Unlike 

 chloroplasts, chromoplasts are of little or no value from the point of 

 view of nutritive metabolism ; inasmuch, however, as they are often 

 responsible for the bright attractive colours of petals and ripe fruits, 

 their ecological importance is considerable. 



Leucoplasts are typically colourless, but frequently possess the 

 capacity of forming colouring matters under certain conditions, and of 

 thus becoming transformed into chloroplasts or chromoplasts. They 

 are commonly minute spherical bodies, but their shape may also be 

 greatly modified by inclusions, consisting of protein-crystals or starch- 

 grains. Leucoplasts are employed for a variety of purposes. In 

 embryonic cells they represent future chloroplasts or chromoplasts, 

 which are still in a non-pigmented juvenile condition. In storage- 

 cells they are responsible for the formation of starch grains at the 

 expense of soluble carbohydrate material, and are hence termed by 



