78 PROBLEMS OF EVOLUTION 



way of explanation of the difficulty. The three commonest 

 buttercups in our grass meadows are Ranunculus bulbosus, the 

 early one with the bulbous root, R. repens and R. acris. When 

 the flower of R. bulbosus opens, the sepals bend backward and 

 downward, and close round the stalk, in the other two species 

 they lie immediately underneath the spreading petals. It is very 

 difficult to feel sure what purpose, if any, they serve in either 

 position. They may possibly in both cases afford some pro- 

 tection against the visits of undesirable insects that crawl up the 

 flower stem. Let us admit this, then, and proceed to the next 

 point. The flower stalks of R. acris are round and have no 

 grooves ; those of the other two are grooved. The grooving, 

 however, is different in the two species. R. bulbosus has five 

 comparatively deep furrows in the stem between the flower and 

 the imperfect leaf below it, so that in transverse section there are 

 five projecting pillars. But two of the furrows have minor ridges 

 running down them, and the latter are sometimes so clearly marked 

 that a transverse section presents a most irregular pentagon. R. 

 repens has five well-marked ridges without the two smaller 

 additional ones. The grooving seems to be of no service, and 

 even if we assume that it is, how did Natural Selection make the 

 two forms of grooving constant specific characters when per- 

 sumably one was as good as the other ? 



No use can be suggested for the callosities on the legs of 

 horses. The wonderful adaptation found in woodpeckers in 

 the feet, tail, and more particularly in the tongue and connected 

 parts are common to the various species. The specific distinc- 

 tions, mainly founded on coloration of plumage are, it is main- 

 tained, of no service. Even genera and families are in many 

 cases separated by characters for which it is often difficult to 

 claim utility. The head of the flower-stalk of the thistle 

 (Car duns) on which the little florets grow is covered with 

 bristles. Onopordon, a nearly allied genus, is distinguished by 

 the absence of such bristles. Two other genera of composite 

 flowers, Hypochxris and Leontodon, are separated from one another 

 for the same reason. You can know the crocodile of the Nile 

 by a tooth in the lower jaw, which, when the mouth is closed, is 



