No. 439-] XORTHER.X GA MOPE TA LOUS FLOWERS. 



457 



tributed as follows: — Monocotyledones 802 green; Apetake 

 134 green, 1 white, 11 yellow, 2 red, and 4 purple; Polypetake 

 27 green, 1 red, and 8 purple; Gam<>petakr 58 green species. 



The Pigments. — The colors of angiospermous plants are due 

 to three groups of pigments, occurring either singly or associated 

 together; the green pigments or chlorophyll; the yellow pig- 

 ments which include carotin, xanthophyll and phyllofuscin ; and 

 the soluble red and blue pigments or anthocyan. 



Chlorophyll. — The characteristic green shades of foliage are 

 caused by chlorophyll, the most common of all plant pigments. 

 With the exception of the Fungi it is found in nearly all forms 

 of vegetation, though its presence is often partially masqued, as 

 in the Algae, by its association with other coloring substances. 

 Its wide distribution is explained by its activity in the synthesis 

 of carbohydrates. According to several late investigators there 

 is more than one kind of chlorophyll. This view was adopted 

 in 1895 by Gautier and Etard. Kohl in his recent work on 

 " Carotin " admits of two varieties, which he designates as a- 

 chlorophyll and /3-chlorophyll. 1 In a green leaf "the normal 

 chloroplasts contain much a-chlorophyll, little /3-chlorophyll, 

 much carotin, little a-xanthophyll, and little /3-xanthophyll." 2 

 The a-chlorophyll is to be regarded as pure chlorophyll. Its 

 absorption bands lie in the red half of the spectrum. The 

 genetic relations of chlorophyll require further investigation. 

 Wiesner's theory that etiolin is the mother substance of chloro- 

 phyll has not been proven ; and, according to Kohl, it can be 

 shown that in the greening of etiolated plants chlorophyll is not 

 formed at the expense of the etiolin. The different shades of 

 green observable in foliage are due partly to the quantity and 

 arrangement of the chloroplasts. The upper side of a leaf is 

 usually a darker green than the lower, because the palisade cells 

 contain three or four times as many chlorophyll granules as the 

 spongy parenchyma of the lower side. 3 Ferns and mosses, 

 which habitually live in shady ravines, are a deeper green in 



