i6o BOTANY AND PHARMACOGNOSY. 



While the protoplasm has been termed by Huxley " The phys- 

 ical basis of life," the c'hloroplastid 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 con- 

 verted 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. 



Chromoplastids. — -In many cases, as in roots, like those of 

 carrot, or flowers and fruits, which are yellowish or orange- 

 colored, there is present a corresponding yellow pigment, and to 

 this class of pigments the name chromophyll may be applied. 

 Some of these pigments, as the carotin in carrot, have been iso- 

 lated in a crystalline condition. 



Chromoplastids usually contain, as first pointed out by Schim- 

 per and Meyer, protein substances 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 differ- 

 ent from the chloroplastids. They are more unstable than the 

 chloroplastids, and are formed in underground parts of the plant, 

 as in roots, 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. 



The PLASTiD PIGMENTS are distinguished from all other color- 

 substances in the plant by the fact that they are insoluble in water 

 and soluble in ether, chloroform and similar solvents. In fact 

 they are but little affected by the usual chemical reagents under 

 ordinary conditions. 



Apart from the difference in color, the yellow pigment (chro- 

 mophyll) is distinguished from the green (chlorophyll) by the 

 fact that the latter is said to contain nitrogen, and also by their 

 difference in behavior when examined spectroscopically, chloro- 

 phyll giving several distinct bands in the yellow and orange por- 

 tion of the spectrum, which are wanting in the spectrum of the 

 yellow principle. 



