Mr. J. Ball on the genus Leontodon, 5 



of the relations of closely allied forms, can we hope to arrive at 

 distinct conceptions of the true nature of those fundamental 

 groups whose existence under the name of species and genus 

 we confidently affirm, but whose essential attributes we find our- 

 selves unable to define a priori, and, still less, to recognize with 

 certainty when presented to us in nature. 



Adopting the definitions which appear to me best suited to 

 the present imperfect state of our knowledge, I distinguish as a 

 species, that group of vegetable forms, of which we are led by 

 observation and analogy to believe, that the differences between 

 the individuals composing it may be made to disappear by the 

 continued agency of external circumstances either upon the in- 

 dividuals themselves or on their descendants. I denominate sub- 

 species a group of similar forms capable of propagation over a 

 definite area, not immediately altered in form by a change in 

 external conditions, but not distinguished by characters usually 

 found to be constant in the same group. In common with most 

 other botanists, I style varieties those diversities of form which 

 are not continued in the descendants of the individual, or which 

 disappear speedily under the influence of new external agencies. 

 As a provision for our ignorance, I distinguish as lusus those 

 unusual conditions in which a marked difierence from the ordi- 

 nary form is exhibited by a small number of individuals, respecting 

 which we are unable to assert whether it be the result of unusual 

 external agency or of some specific or subspecific difiference of 

 organization. 



Denoting that which appears to be the typical form of each 

 species by the Roman capital A, and premising that in all cases 

 I distinguish the subspecies by a Roman capital, and the corre- 

 sponding variety by the small Roman letter, I propose the fol- 

 lowing symbols, which appear to be appropriate not only for the 

 genus Leontodon, but for the entire natural order of Cichoracea. 



4-D ; stem or scape more divided, capitula more numerous. 

 — D ; stem or scape less divided or simple. 



-fE; plant more slender, leaves and divisions more acute, phylla- 

 ries narrower, florets less numerous. 



— E ; scape thicker, leaves broader, more blunt, phyllaries broader, 



florets more numerous. 

 + P ; involucre clothed with long hairs, usually of dark fuscous 



colour. 

 + G; whole plant more glabrous, or entirely devoid of pubescence. 



— G; pubescence more abundant. 

 + 1 ; leaves more deeply cut. 



— I ; leaves less deeply cut or quite entire. 



Where a subspecies or variety appears to differ from the typical 



