78 Kraemer : Color in plants 



which are much smaller than the nucleus and are distributed 

 through the protoplasm in relatively large numbers. Of these 



there are two distinct groups, one containing a green pigment, 



which gives the green color to leaves, known as the chloroplastid, 

 and the other containing a yellow pigment, which gives the yellow 

 color to yellow flowers and fruits, known as a chromoplastid. In 

 the vacuoles already referred to occur various coloring principles 

 which are dissolved in the cell-sap and which give the various 

 colors other than yellow to flowers and fruits, as blue in the violet 

 or plum, red in the carnation, rose or apple, etc. 



Plastids and plastid color-substances 



Regarding the structure of the plastids we know but very 

 little. In all cases they consist of a protoplasm-like substance in 

 which is held either mechanically or in chemical combination the 

 green or yellow coloring principle. The chloroplastids in addition 

 contain starch-grains, which are considered to be manufactured by 

 the chloroplastid under the influence of sunlight from water and 

 the carbon dioxide of the air ; they may also contain proteid sub- 

 stances and oil. While the protoplasm has been termed by 

 Huxley " the physical basis of life," this little chloroplastid, but 

 the one five -thousandth of an inch in diameter, has been spoken of 

 as the mill which supplies the world with its food, for it is by the 

 process of photosynthesis that the energy of the sun is converted 

 into vital energy, and starch and other products formed, which 

 become not only the source of food for the plant itself, but also 

 the source of the food-supply of the animals which feed upon 

 plants. In other words, horse-power is derived from the energy 

 of the sun which is stored by the chloroplastids in the plant. 



In the chromoplastid, on the other hand, there are usually 

 present, as first pointed out by Schimper and Meyer, protein sub- 

 stances in the form of crystal-like bodies ; starch-grains may also 

 be present. The chromoplastids are very variable in shape and in 

 other ways are markedly different from the chloroplastids. They 

 are more unstable than the chloroplastids, are formed in under- 

 ground parts of the plant, as in the root of carrot, as well as in 

 parts exposed to the light, as in the flower. Their formation 

 frequently follows that of the chloroplastids, as in the ripening of 

 certain yellow fruits, such as apples, oranges, persimmons, etc. 



