1864.] 



Presidents Address* 



609 



the most masterly treatise on any brancli of vegetable physiology that 

 has ever appeared. ' The objects which the author had in view in enter- 

 ing on a comprehensive study of the sexual system of Orchideae, were to 

 show that the contrivances by which they are fertilized are as varied 

 and almost as perfect as any of the most beautiful adaptations of the 

 animal kingdom, and that these contrivances have for their main object 

 the fertilization of one flower by the pollen of another. In pursuance 

 of this object Mr. Darwin set himself to investigate, first, the structure 

 and development of the flower of living specimens of nearly every British 

 species ; secondly, to observe how impregnation was naturally eflected 

 in each ; thirdly, to make a similar structural investigation of the prin- 

 cipal exotic forms ; and, fourthly, to ascertain by experiment the method 

 by which these also are in all probability fertilized. To these investi- 

 gations Mr. Darwin brought all the resources of a most skilful micro*' 

 scopic dissector, of an unwearied and exact observer, of a sagacious 

 experimentalist fertile in resources, of an entomologist versed in the 

 structure and habits of insects, and of an excellent judgment in inter- 

 preting obscure phenomena, and drawing from them correct conclusions. 



The result is a work no less remarkable for the novelty of its facts, 

 and for the importance of their bearing, than for its being the first 

 which correlates the structure with the functions of the floral organs 

 of one of the largest and most conspicuous of the families of plants. 

 It would not be difficult to justify this strong encomium by examples 

 of great interest taken from the work itself, but it would be incom- 

 patible with the limits of this Address ; suffice it therefore to say, that 

 the general conclusion to which Mr. Darwin arrives is, that all the forms, 

 even the most grotesque, which the floral organs of Orchids possess, are 

 directly and obviously of use, and that every structural and physio- 

 logical modification, however minute, tends, with scarcely an exception, 

 to ensure the fertilization of the ovules of one plant by the pollen of 

 another. 



Mr. Darwin's next contribution to physiological botany is entitled 

 " On the two forms, or dimorphic condition, in the species of Primula, 

 and on their remarkable sexual relations." The phenomenon of there 

 being two distinct forms of flower in the genus Primula has long been 

 familiar to naturalists, but the real nature of the difierence between 

 them, and of their respective functions, had not occurred to anyone. 

 Mr. Darwin first suspected that the relations between the forms might 

 be sexual, and he has since, with consummate skill, incontrovertibly 

 proved this to be the case. By a most searching examination of a vast 

 number of specimens of each form, in cultivated varieties as well as in 

 species, he found that, in all, the two forms presented in their stigmatic 

 surfaces, ovules, and pollen, constant diff'erences, unbroken by a single 

 instance of transition between the distinct forms. By experiments 

 continued for several years, he proved that in this genus complete fer- 



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