178 THE STRUCTURE OF FLOWEKS. 



decolorised by exposure to light, are formed in relatively 

 greater amount when the flowers are grown in the dark. 

 This is easily explained if we assume that a higher vital 

 power, depending on the presence of light, is necessary to 

 overcome the more powerful chemical aflBnities of the less 

 stable compounds." 



The crossing of flowers is well known, and much practised 

 by florists, to enhance the variety of tints. The interpreta- 

 tion is that crossing is a stimulating process, and provokes 

 the petaline energy to a high degree. 



From the preceding remarks it will be now gathered 

 that colours, per se, are a result of nutrition ; and that the 

 prevalence of brighter colours in conspicuous flowers which 

 are regularly visited by insects is due to the stimulating 

 effects which they have produced, thereby causing more 

 nutritive fluids to pour into the attractive organs. 



Besides, however, this general i-esult of brilliant colouring 

 there are those peculiar and special displays of bright tints 

 distributed in spots and streaks in certain and definite places 

 only. These have been called " guides " and " path-finders," 

 as they invariably lead to the nectaries. If the theory be 

 true which I am endeavouring to maintain throughout this 

 book, all these effects are simply the direct results of the 

 insects themselves. The guides, like obstructing tangles of 

 hair and nectaries, are always exactly where the irritation 

 would be set up ; and I take them to be one result of a more 

 localized flow of nutriment to the positions in question. 



Instead, therefore, of a flower having first painted a petal 

 with a golden streak to invite the insect, and to show it the 

 right way of entering, the first insect visitors themselves 

 induced the flower to do it, and so benefited all future 

 comers. 



The Oeigin op Coloues. — Mr. Grant Allen has written 



