100 Riley Some Interrelations of Plants a ml 



particular case, out of the question, and that the development 

 of the seed in this species is exclusively due to the stimulation 

 of the tissues caused by the puncturing of the Blastophagas : in 

 other words, that these insects actually represent the male ele- 

 ment in the fertilization. This is certainly the most extraordi- 

 nary phenomenon in the history of fertilization, and if confirmed 

 and Dr. Cunningham has been most careful and circumspect in 

 his work it will give a more striking instance than any we have 

 hitherto obtained of the mutual interdependence which plants 

 and insects may attain and the surprising manner in which they 

 may modify each other. 



GENERALIZATION. 



The peculiarities which I have endeavored to present to you 

 are full of suggestion, particularly for those who are in the habit 

 of looking beyond the mere facts of observation in endeavors 

 to find some rational explanation of them ; who, in other words, 

 see in everything they observe significances and harmonies not 

 generally understood. The facts indicate clearly, it seems to me, 

 how the peculiar structures of the female Pronuba have been 

 evolved by gradual adaptation to the particular functions which 

 we now find her performing. With the growing adaptation to 

 Pronuba's help, the Yucca flower has lost, to a great extent, the 

 activity of its septal glands ; yet coincident with it we find an in- 

 crease in the secreting power of the stigma. This increase of the 

 stigmatic fluid has undoubtedly had much to do with originally 

 attracting the moth thereto, while the pollinizing instinct doubt- 

 less became more and more fixed in proportion as the insect lost 

 the power or desire of feeding. With the mind's eye I can look 

 back into the past and picture the gradual steps by which the Pro- 

 doxids to which I have alluded have differentiated along lines 

 which have resulted in their present characteristics. On the one 

 side I see variations which have become sufficiently fixed to be 

 considered specific ; yet which can have no especial 1 tearing on the 

 life necessities of the species, but are a consequence rather of 

 that universal tendency to variation with which every student 

 of Nature becomes profoundly impressed. Thus the wing-mark- 

 ings vary from a darker general coloring, as in Prodoxus senescent, 

 to a more uniform intermixture of the black scales among the 

 white, as in c/m /v;//.s, or a sparser intermixture thereof, as in [mlcer- 

 iilr.iifu*. The disposition of the black scales is in spots or bands. 

 whether transverse or longitudinal, as in marginalus^ reticulatw, 



