THE PLASTIDS 9 



guises and performing different functions, for the leucoplasts 

 may become chloroplasts and the chloroplasts chromoplasts. 

 This fact is well made out in the tomato, for instance, where the 

 very young pistil in the bud contains no other plastids than the 

 leucoplasts and is colorless in consequence; later when the corolla 

 drops away and the pistil emerges into the light the leucoplasts 

 produce chlorophyll and the young fruit is green; but when the 

 fruit begins to ripen the chlorophyll is gradually replaced by 

 red and orange coloring matters, and the chloroplasts become 



Fig. 2. — A, cell from the epidermis of the upper side of the calyx of Tropseolum majus 

 with crystalline chromoplasts; B, cells fromi the petal of Lupinus luteus with yellow chro- 

 mopldsts; C, cell showing numerous chloroplasts scattered through the cytoplasm. {A, 

 after Strasburger; B, after Frank.) 



chromoplasts. The leucoplasts are therefore the progenitors 

 of the other plastids, but they have their own functions to per- 

 form as leucoplasts: they take carbohydrates out of solution 

 in the cell-sap and store these within themselves in the form of 

 insoluble starch grains. This is well seen in those cells and 

 tissues, as in the potato and the endosperm of seeds, where 

 reserve food is stored away. The chloroplasts secrete two color- 

 ing matters known as chlorophyll-green and carotin or chlorophyll- 

 yellow. The chloroplasts employ these pigments in arresting the 

 sun's energy, by means of which they make the food of the plant. 



