148 CORRELATED VARIATION. Cuap. V. 



eaters, etc.), these are likewise the most abnormal in tlieir 

 teeth. 



I know of no case better adapted to show the importance 

 of the laws of variation and correlation, independently of util- 

 ity and therefore of natural selection, than that before referred 

 to, of the difference between the outer and inner flowers in 

 some Conipositous and Umbelliferous plants. Every one knows 

 the dilTercnce in the ray and central florets of, for instiuice, th{^ 

 daisy, and this difference is often accompanied with the partial 

 or complete abortion of the rejoroductive organs. But in some 

 of these plants, the seeds also differ in shape and sculpture. 

 These differences have been attributed by some authors to the 

 I^rcssure of the involucra on the florets, or to their mutual press- 

 in-e, and the shape of the seeds in the ray-florets of some Com- 

 positie countenances this idea; but with the Umbellifene, it 

 is by no means, as Dr. Hooker informs me, the species with 

 the densest heads Avhich most frequently differ in their inner 

 and outer flowers. It might have been tliought that the de- 

 velopment of the ray-pc^tals by drawing- nourishment from the 

 r(>productivc organs had caused their abortion ; but this can 

 hardly be the S(jle cause, for in some Compositir; the seeds of 

 the outer and inner florets differ without any difference in the 

 corolla. Possibly these several differences may be connected 

 Avith the diflcrent flow of nutriment toward tlie central and 

 external flowers : we know, at least, that, with normally iireg- 

 ular flowers, those nearest to the axis are most subject to 

 jK'loria, that is, they become S3'mmetrical. I may add, as an 

 instance of this, and of a striking case of correlation, that I 

 have recently observed in many pelargoniums, that in the cen- 

 tral flower of the truss the two upjier petals often lose their 

 ])atches of darker color; and when this occurs, the adherent 

 nectary is qviite aborted. When the color is absent from only 

 one of the two upper petals, the nectary is not quite aborted, 

 but is much shortened. 



With respect to the developmoit of the corolla in the cen- 

 tral and exterior flowers, Sprengel's idea that the ray-florets 

 serve to attract insects, whose agency is highly advantageous 

 or necessary for the fertilteation of these plants, is highly jirob- 

 able ; and if so, natural selection may have come into i^lay. 

 ]>ut, witli respect to the seeds, it seems impossible that their 

 diiVcrences in shape, which ai-e not ahvaj's correlated with any 

 difference in the corolla, can be in any way beneficial : yet in 

 the Umbellifere these differences arc of such apparent impor- 



