THE CELL. 83 



masses (Fig. 190) ; in JJloihix, also a fresh-water Alga, 

 it is iu the form of a riug or zone. It is very seldom, 

 though sometimes, fouud dissolved in the cell. The chloro- 

 phyll is soluble in alcohol, ether, chloroform, etc., and 

 when removed by these solvents a protoplasmic body 

 remains behind. The chlorophyll thus extracted has 

 recently been obtained in the form of crystals. Only cells 

 exposed to the light have chlorophyll developed in them. 

 If chlorophj-ll-bearing cells be placed in the dark, they 

 gradually lose their green color. If the plant food be 

 deprived of iron, the chlorophyll will not be developed. 

 The importance of this compound is great, for only in cells 

 containing chlorophyll (and exposed to sunlight) does 

 assimilation — which is the change of the crude sap, or 

 inorganic food, into organic matter — take place. Those 

 plants are destitute of chlorophyll which do not assimilate 

 food, but absorb it, already " digested" (assimilated), from 

 others ; for example, parasitic plants (Fungi, etc.). 



io6. The following are regarded as modifications of 

 chlorophyll : xanthophyll, which is the yellow coloring 

 matter of the autumn leaves; anthozanthin is the color- 

 ing matter of the yellow petals of flowers ; phycozanthin 

 is a brown coloring matter associated with chlorophyll in 

 many Algse, as in Diatoms and Fucus ; phycocyan is 

 the blue coloring matter in the cells of Nostocs ; phyco- 

 erythrin is the red coloring matter of the Red Algse. 

 The last two are soluble in water. The red orange and 

 yellow coloring matters of flowers are found in the form of 

 rounded protoplasmic bodies. Other coloring matters are 

 dissolved in the cell-sap, as many which are found in 

 flowers. Of this kind also is the red of many autumn 

 leaves, as the Cornus and Ampelopsis. The pigments of 



