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fertilization. Many colors are better than one since the flowers 

 are rendered more conspicuous by contrasts with each other as 

 well as with the foliage, and insects are less liable to visit them 

 indiscriminately. The sequence of colors, green, yellow, white, 

 red, purple, and blue depends upon physiological causes. Plants 

 vary greatly in their capability of forming the different kinds of 

 pigments, and the floral colors are correlated with the variability 

 of this function. The primitive colors green, yellow and white 

 have been determined by the nature of the chloroplast and its 

 pigment content ; while red. purple and blue have arisen as the 

 result of various chemical and physical conditions. 



Bibliography. — In the preparation of these papers constant 

 use has been made of the works of Miiller, Knuth, Kerner. and 

 Darwin; of the Manuals of Gray and Chapman; and of the 



