5*4 



NATURE 



[Sept. 27, 1883 



the first appearance of vegetation to aquatic forms. With 

 the change to dry localities, from the vascular Cryptogams 

 seem to have been developed wind-fertilised unisexual 

 flowers — thus first the Gymnosperms, and from these 

 afterwards the Angiosperms have arisen. Finally from 

 the wind-fertilised Angiosperms entomophilous flowers 

 arose ; insects came first accidentally and afterwards 

 regularly to seek their food on flowers, and natural 

 selection fostered and perfected every change which 

 favoured insect visits, and thereby aided cross-fertilisa- 

 tion. With the transition to insect-fertilisation came on 

 the one hand great economy of pollen, but on the other 

 hand the uncertainty of insect visits made it as a rule 

 necessary that self-fertilisation should remain possible. 

 Thus, though descended from unisexual (anemophilous) 

 ancestors, entomophilous flowers are usually herma- 

 phrodite, and are capable to a great extent of ferti- 



lising themselves when insect visits fail. But in the 

 course of further development many of them have so 

 increased their means of attracting insects (by colour, 

 perfume, honey, &c.) that the power of self-fertilisation 

 has become superfluous, and finally has been lost. 

 Insects, in cross- fertilising flowers, endow them with off- 

 spring, which, in the struggle for existence, vanquish 

 those individuals of the same species which are the off- 

 spring of self-fertilisation. The insects must therefore 

 operate by selection in the same way as do unscientific 

 cultivators among men, who preserve the most pleasing 

 or most useful specimens, and reject or neglect the 

 others. In both cases selection in course of time brings 

 those variations to perfection which correspond to the 

 taste or to the needs of the selective agent. Different 

 groups of insects, according to their sense of taste or 

 colour, the length of their tongues, their way of move- 



Primula inUgrifolia,\j. A.— Short-styled, B.— Long-styled plant (nat. size). C— Short-styled, D.— Long-styled fljwerin section (nat. siie). E.— 

 Stigmatic papillae of short-styled flower. F, G. — Ditto oflong-styled flower. H.— Stigma of short.styled flower, I. — Ditto of long-styled flower 

 (x 7). K. — Moistened pollen of short-styled flower, L.— Ditto oflong-styled flower. 



ment, and their dexterity, have produced various odours, 

 colours, and forms of flowers, and thus have flowers and 

 insects progressed together towards perfection. All this 

 leads on to the final proposition with which this general 

 retrospect ends, that the forms, colours, and odours of 

 the flowers in a particular region must depend in the 

 closest manner upon the insect fauna of the region, and 

 especially upon the relative abundance of the various 

 classes of insects in it. 



The whole subject of the fertilisation of flowers is one 

 of still unexhausted resources. The student will in this 

 volume have references to what is known, and will find 

 out easily the immense amount of details still waiting in- 

 vestigation. An almost new subject is one that has been 

 lately referred to in our columns by Prof. A. W. Bennett, 

 on the constancy of insects in their visits to flowers ; and 

 several new lines of research are pointed out in Mr. 

 Darwin's preface. It is a subject within the reach of all 



honest, patient observers. It is limited practically to no 

 clime and season. Some of Miiller's observations were 

 made on flowers grown in windows, and all were carried 

 on amid the somewhat scant leisure of a busy profes- 

 sional life. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

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 No notice is taken of anonymous communications. 



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Iguanodon 



Since I wrote the account of M. Polio's researches on 

 Iguanodon, which appeared in NATURE of September6 (p. 439), 

 I have had the advantage "f >-ine conversation with Prof. Marsh 



