vi COLOURS OF PLANTS 405 



and hazel, our nettles, grasses, sedges, and many others. In 

 some of these the male flowers are very conspicuous, as the 

 catkins of the willows, and these secrete honey and attract 

 numerous insects at a season when there are few other flowers, 

 and thus secure cross -fertilisation. Sedges and grasses are 

 also occasionally visited by insects. 



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 vege- 

 table 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 modification of leaf -texture, 

 such as occurs in the petals and coloured sepals of flowers. 

 Wind -fertilised plants never have such specially organised 

 floral envelopes, and, in most cases, are entirely without a 

 calyx or corolla. The connection 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 varie- 

 gated flowers of such groups as the Scrophularinese and 

 Orchideae. The same laws as to the conditions of a maximum 

 production of colour are thus found to obtain both in plants 

 and animals. 



Relation of the Colours of Flowers and their Geographical 

 Distribution 



The adaptation of flowers to be fertilised by insects 

 often to such an extent that the very existence of the species 

 depends upon it has had an important influence on the dis- 

 tribution of plants and the general aspects of vegetation. 



