Ill THE COLOURS AND PIGMENTS OF PLANTS 71 



species of orchids, and on the corolla of the foxglove. 

 There seems little doubt that these markings are in 

 many cases employed by insects as landmarks in 

 their search for honey, and they have been in con- 

 sequence termed honey-guides. In many cases, how- 

 ever, they are much more complex than seems 

 necessary for this function, and are by no means 

 limited to flowers containing honey ; their meaning 

 and origin are still very doubtful. 



Meaning of Plant Pigments and Summary 



Looking at the colours of flowers and fruits as a 

 whole, we may say that all the processes which give 

 rise to their brilliant colours have a parallel in the 

 vegetative shoot. The prominence of lipochromes 

 and the development of anthocyan are paralleled in 

 the autumnal coloration of leaves. The development 

 of a white colour is paralleled by the occasional 

 partial albinism of leaves, which occurs either as a 

 result of injury by other organisms, or in some 

 instances as a natural condition, e.g. in the lung- 

 wort {Pulmonarid). Even the complex markings of 

 petals are dimly foreshadowed in the veining of 

 leaves. 



All this is fairly obvious, but when we attempt 

 to discuss further the prime meaning of colour in 

 plants, the difficulties are very great. Of the five 

 groups of pigments described in the last chapter, we 

 have in plants the first represented by chlorophyll ; 

 the third possibly represented by the anthocyan 

 pigments, which are apparently derived from tannins, 

 and are probably useless substances ; the fourth. 



