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POPULAR SCIENCE MONTHLY. 



phyll against the more intense action of the rays. It is also in 

 this purpose of protection of the chlorophyll that many of the 

 colors grouped under anthocyan find their chief function in the 

 plant. In such instances the color is generally in solution in 

 the sap of the layers of cells exterior to the chlorophyll, and 

 light must pass through the coloring matter in order to reach 

 the interior of the leaf. This may be seen by reference to 

 Fig. 4, in which is shown a cross-section of a portion of a leaf of 

 coleus. 



That such layers of coloring matter do materially alter the 

 light which passes through them may be demonstrated if the spec- 

 trum of light which has passed through a solution of them is 

 examined in the manner described above. Water, instead of alco- 

 hol, is used as a solvent, 

 however. If the color of 

 the leaf of the amaranth 

 is used, it will be found 

 that nearly all the light 

 has been absorbed ex- 

 cept a portion between 

 B and D (Fig. 1, II). 



It may be seen that 

 a large proportion of 

 the light is absorbed by 

 the anthocyan and con- 

 verted into heat, and 

 furthermore it is inclu- 

 sive of the portion of 

 the spectrum which ex- 

 ercises the most violent 

 disintegrating effect on 

 chlorophyll, as may be 

 seen by reference to Fig. 

 2. The portion which 

 promotes synthesis of food materials, on the other hand, is trans- 

 mitted almost unchanged to the chlorophyll beneath. That the 

 anthocyan does partially retard the disintegration of chlorophyll 

 by light may be seen if two vessels containing solutions of chloro- 

 phyll are so arranged that the light which strikes on one of them 

 shall first pass through a parallel- walled vessel containing water, 

 and that which strikes the other through a similar vessel con- 

 taining a solution of anthocyan. The chlorophyll in the first will 

 soon become much more discolored than in the second, which has 

 received light transmitted through anthocyan. The number of 

 plants in which coloring substance is present in the cell sap or 

 walls of the outer layers of leaves is extremely large, and em- 



Fig. 4. Cross-section of Leaf of Coleus. A, A, epi- 

 dermal cells filled with reddish cell sap ; B, cells con- 

 taining chlorophyll bodies. 



