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THE AMERICAN NATURALIST. [Vol. XXXVII. 



panied by yellow. In the aquatic Alismaceae the entire nineteen 

 species are white, and in the Caryophyllacese there are fifty-six 

 white flowers but no indigenous yellow species. The six species 

 of the Xyridaceae on the other hand all produce yellow flowers. 

 In the anemophilous Betulaceae there are eleven yellow species, 

 but flowers with a yellow calyx are rare in the Apetalas. The 

 Ilypericaeex are nearly monochromatic as twenty-two species 

 are yellow and only two red. The zygomorphic Orchidaceae con- 

 tain ten yellow-flowered species, a larger number than any other 

 monocotyledonous family. A surprisingly large number of yel- 

 low flowers occur in the zygomorphic Papilionaceas (33 species), 

 the Scrophulariaceae (33 species), and the Eentibulariaceae (11 

 species). This fact Miiller attributes, and we think rightly, to 

 the persistence of the primitive yellow in certain genera, and its 

 little tendency to variation with the specialization of the flowers. 

 In many families of the Gamopetake yellow flowers are absent, 

 or are represented only by a single species, as in the orders E/i- 

 cales, Ebenales, and Gentianales, where the inflorescence is 

 chiefly white or red. 



White Flowers.— White flowers are most abundant in the 

 American as well as in the European flora. A white inflores- 

 cence is evidently a less tax on the energies of a plant than one 

 containing pigments ; and trees and shrubs, which produce their 

 flowers in almost boundless profusion, as the Pomacea:, Drup- 

 aceae, Ilicaceae, and the genus Viburnum, have almost exclusively 



marilydue to degeneration. In this connection the studies of 



show evidences^ degeneration, are of interest. According to 

 their investigations such leaves are thinner than normal green 

 leaves, and consist wholly of cellular tissue with the palisade 

 cells absent. It is desirable to consider very briefly some of the 

 conditions under which white flowers occur, and under which 

 they develop chromatism. They are derived both from primi- 

 tively green and from high colored flowers. Small, densely 

 clustered white flowers are common in the Crucifene, Saxifrag- 

 aceas, Umbelliferae, Cornacerc and Ericaceae. In these^flowers 

 the stimulus to produce pigments is wanting and the leaf-green 



