92 TEXTBOOK OF BOTANY 



stances formed by the decay of the insects pass into the leaf tissues and 

 may be used as food. These plants, however, grow just as well in the 

 absence of insects. 



Fig. 49. The tall southern pitcher plant {Sarracenia flava), commonly called 

 trumpet leaf. Photo by G. W. Blaydes. 



Chemical differences. Some plants are noted for their anthocyanin 

 pigments. The patterns in which these pigments are arranged in the 

 leaves of coleus exemplify the fact that although the cells of the leaf 

 primordia are all alike, the cells derived from them differentiate not only 

 structurally but chemically. Some of the pigments in these leaf color 

 patterns may be in the epidermis, while others are in the mesophyll in 

 one part of the leaf but absent in other parts. Experiments have shown 

 that the inheritance of certain factors determines both pigment forma- 

 tion and patterns. Cells of certain areas behave diflFerently from corre- 

 sponding cells in other leaf areas. Evidently the tissue systems of the 

 whole leaf react on the individual cells. The leaf, therefore, is not just a 

 mass of independent units. 



Another example of hereditary differences in the chemical compounds 

 formed in leaves is furnished by two closely related plants, spearmint 

 and peppermint, each producing a characteristic aromatic oil used in 



