234 TROPICAL NATUEE, AND OTHER ESSAYS. 



sedges, and many others. In some of these the male 

 flowers are, it is true, conspicuous, as in the catkins of 

 the willows and the hazel, but this arises incidentally 

 from the masses of pollen necessary to secure fertiliza- 

 tion, as shown by the entire absence of a corolla or of 

 those coloured bracts which so often add to the beauty 

 and conspicuousness of true flowers. 



The Same Theory of Colour Applicable to Animals 

 and Plants. — It may be thought that this absence of 

 colour where it is not wanted is opposed to the view 

 maintained in the earlier part of the preceding chapter, 

 that colour is normal and is constantly tending to appear 

 in natural objects. It must be remembered, however, 

 that the green colour of foliage, due to chlorophyll, 

 prevails throughout the greater part of the vegetable 

 kingdom, and has, almost certainly, persisted through 

 long geological periods. It has thus acquired a fixity 

 of character which cannot be readily disturbed ; and, as 

 a matter of fact, we find that colour rarely appears in 

 plants except in association with a considerable modifica- 

 tion of leaf-texture, such as occurs in the petals and 

 coloured sepals of flowers.. Wind-fertilized plants never 

 have such specially organized floral envelopes and, in most 

 cases, are entirely without a calyx or corolla. The con- 

 nection between modification of leaf-structure and colour 

 is further seen in the greater amount and variety of 

 colour in irregular than in regular flowers. The latter, 

 which are least modified, have generally uniform or but 

 slightly varied colours ; while the former which have 

 undergone great modification, present an immense range 

 of colour and marking, culminating in the spotted and 

 variegated flowers of such groups as the Scrophularinese 



