HARDWICKE'S SCIENCE-GOSSIP. 



i6i 



colours in other parts of the vegetable kingdom. It 

 is difficult to see what bearing these facts are 

 supjjosed to have upon the insect-selection theory, 

 other than the light they may throw on the 

 chemical origination of the colours of flowers, since 

 tliese are in many cases produced by the same or 

 allied pigments. Most of the colours mentioned by 

 ^Ir. Robertson are caused by products of destructive 

 metabolism, or by products incidental to constructive 

 jihysiological processes : some have themselves a 

 distinct physiological significance — e.g., the colouring 

 pigments of the red and brown Fuci and other algoe, 

 which are assimilative pigments. Now it is out of 

 the question that the colouring pigments of flowers 

 are merely incidental products of physiological pro- 

 cesses, though no doubt they were originally such ; 

 it is clear that they now have a physiological 

 significance of their own. Can there be any reason- 

 able doubt that their function is to attract insects, 

 assuming the benefits of cross-fertilisation ? Further, 

 this explanation cannot apply to any of the other 

 instances of bright colour mentioned. They cannot 

 possibly have any connection with insects. 



If this be so, and it cannot be otherwise, Mr. 

 Robertson's question : — " By what process of insect- 

 selection have these colours been evolved ? " — needs 

 no answer. Insect-selection, which at least may 

 have something to do with the colours of flowers, has 

 not nor can have the slightest connection with these 

 other colours. To borrow and adapt an illustration 

 used by Mr, Robertson, it would be just as reason- 

 able to object to the insect-selection theorj', on the 

 ground that we cannot explain by it the colours of 

 " Orient gems," as on the ground that we cannot 

 explain by it the other bright colours of the vegetable 

 world ; for, from this point of view, the latter have 

 just as little connection as the former with the colours 

 of flowers. For a somewhat fuller discussion of this 

 point, viz., the essential difference between the 

 colours of flowers on the one hand, and colours 

 produced by pigments, which are mere incidental 

 products of physiological processes, and have no 

 physiological significance of their own, I will refer 

 Mr. Robertson to my last paper, Science-Gossip for 

 Feb. (pp. 25, 26). 



I am at a loss to understand the meaning, from an 

 €volutionary point of view, of Mr. Robertson's 

 question :— " Can it be argued that the highest foims 

 were created destitu'e of their most attractive 

 features, until fortuitously visited by the wandering 

 bee?" Mr. Robertson talks of "attractive 

 features ; " he must remember that each of the 

 other colours he has mentioned has an explanation, 

 either as caused by a product of metabolism, or 

 as having a physiological significance of its own ; 

 and that their " attractiveness " is an explanation of 

 none of them (except those of fruits and seeds, which 

 are adaptations for dispersal by birds, etc.). On the 

 other hand, if he admit?, as he must, that in their 



attractiveness lies the physiological significance of 

 the colours of flowers, it must be plain that, from an 

 evolutionary point of view, the colours of flowers 

 could not have been permanently developed before 

 their function was existent ! Surely Mr. Robertson is 

 familiar with the fact that at one time phanerogamous 

 plants did not exist ; that the primitive phanerogams 

 were anemophilous ; and finally that entomophily is 

 only a recent devolopment of the mechanism of cross- 

 fertilisation. And since, as I have said, the colours 

 of flowers could have no function before entomophily 

 became general, it becomes clear that though the 

 hypothesis that "the highest forms were created 

 destitute of their most attractive features " may be 

 a " myth worthy of arm-chair theorists," that the 

 foliar structures surrounding the proper reproductive 

 organs of primitive phanerogams were permanently 

 coloured, or partook in any way of the nature of 

 an entomophilous perianth, is an evolutionary 

 impossibility. 



I must confess that I do not fully understand the 

 drift of the whole of Mr. Robertson's argument 

 about the relations of long- and short-tongued insects 

 to flowers and to each other, but much of it is clearly 

 based on misconception. Thus, for instance, Mr. 

 Robertson has apparently argued upon the 

 assumption that if certain flowers have benefited 

 by increasing complexity, all flowers remaining 

 primitive ought to have been eliminated in the 

 struggle for existence. He should remember that the 

 function of a flower is to carry on the process of 

 reproduction, and that there are many different ways 

 of perfecting the discharge of this function. Thus, 

 Miiller : — "The dependence of entomophilous 

 flowers on guests so infinitely various in habits, 

 tastes, and numbers, in their food and in the means 

 of obtaining it, must have rendered possible 

 not one but countless paths towards perfection, 

 paths leading not always forwards but sometimes 

 backwards ; and only in such a way could the 

 infinite variety of existing flowers have come 

 into existence." The advantages of primitive open 

 flowers, with honey and pollen unconcealed, lie 

 in the great number of insects of all descriptions 

 attracted (when the flower is large and conspicuous), 

 and thus the strong probability at least of cross- 

 fertilisation being effected. The disadvantages, on the 

 other hand, are great, as large quantities of pollen 

 have to be produced, to make up for that stolen by 

 pollen-eating insects, and to ensure the bodies of the 

 visitors getting well covered with it. Further self- 

 fertilisation is effected by the visitors climbing from 

 the anthers to the stigmas just as often as cross- 

 fertilisation. Now in the case of highly-specialised 

 flowers adapted for long-tongued insects only, there 

 is certainly the chance of the flowers not being visited 

 at all ; but, in most cases, if an insect thrusts its 

 proboscis into two flowers consecutively, cross- 

 fertilisation must take place, which is far from beitig 



