RILEY — GENUS PRONUBA ; FERTILIZATION OF YUCCA. 57 



secondly, there is much yet to learn of these habits, and I wish to 

 draw the attention of entomologists to the subject. 



Of late years, and more especially since the publication of Mr. 

 Chas. Dai-win's interesting work on the fertilization of Orchids,* 

 we have come to understand more and more the important part 

 which insects play in the fertilization of plants ; and the old idea, 

 that color and perfume in flowers were intended for man's espe- 

 cial pleasure, is giving way to the more natural and philosophic 

 view that they are useful to the plants by attracting the needed 

 insects. 



In Dr. Asa Gray's recent little work, " How Plants Behave," 

 etc., instances enough are given, in an admirably plain and lucid 

 style, to show the manner in which many flowers are curiously 

 and elaborately constructed so as just not to do of themselves 

 what must necessarily be done for them in order to prevent de- 

 generacy or extinction of the species. Some plants, as Fritz 

 Miiller proved, are so self-impotent that they never produce a 

 single seed by aid of their own pollen, but must be fertilized by that 

 of a distinct species or even of a supposed distinct genus ; while 

 in some cases the pollen and stigma mutually act on each other in 

 a deleterious manner. f The wind is an important agent in the 

 fertilization of certain plants, and some are fertilized even by 

 the higher animals ; but by far the greater number are fertil- 

 ized, or more strictly speaking pollenized, by insects ; while the 

 number of species (termed Entomophilce by Delpino) which 

 absolutely depend for pollenation on insect agency is not in- 

 considerable. These insect pollenizers belong to several Orders, 

 but mostly to the Hymenoptera and Lepidoptera. A familiar 

 example is furnished by our milk-weeds (^Asclepias), the pollen- 

 masses of which may often be found adhering in pairs to the legs 

 of bees and other insects, and sometimes in such quantities as to 

 prove a real detriment and incumbrance to the bearers. Every 

 year I receive specimens of such pollen-burdened bees, which are 

 generally supposed to be infested with some parasite ; and Mr. 

 Jas. D. Meador, of Independence, lately sent me a very gloomy 

 account of the dangerous condition of his apiary from this cause. 

 Each of the numerous flowers which constitute the well-known 



* On the various Contrivances by which British and Foreign Orchids are fertilized by 

 Insects. London, 1S63. 



t See Darwin's "Animals and Plants, etc.," II. p. 133. 



