ON THE INHERITANCE OF CERTAIN CHARACTERS 

 IN THE COMMON GROUNDSEL — 5^iV^^C70 

 VULGARIS, LINN.— A^D ITS SEGREGATES. 



By A. H. TROW, D.Sc, F.L.S. 



Introduction. 



The common groundsel is a plant of world-wide distribution and 

 one might reasonably expect that its various forms would be well known 

 to botanists. In Koch's Synopsis, Ed. III. 1902, two varieties only are 

 recognised, sordidus and radiatus, and the descriptions are unfortunately 

 too brief and too vague to be of much value. Rouy, in the Flore de 

 France, Vol. viTi, p. 343, adds two more — crassifolius and Motelayi, 

 which are also badly defined and inadequately investigated. The 

 majority of botanists recognise two forms only : (a) the type form 

 S. vulgaris, Linn, which is non-radiate, and (6) a variety of this with 

 ligulate ray florets, 8. vulgaris, Linn., var. radiatus, Koch. 



It is noteworthy that although the Compositae constitute about 

 one-tenth of the phanerogamic flora of the world, they have received 

 comparatively little attention so far from those who are engaged in 

 experiments on plant breeding. 



Moreover, numerous plant hybrids are recognised in every modern 

 flora, but comparatively few of them have hitherto been tested by the 

 methods of genetics. 



Certain plant genera, such as Hieracium, Rosa and Rubus have 

 been studied intensively to such an extent that old well-known species 

 like Ruhus fruticosus and Rosa canina have been split up into numerous 

 smaller units recognisable with certainty only after much painstaking 

 study, yet there has been practically little effort, except in Hieracium, 

 to trace by experimental means the genetic relationships of such forms. 

 Indeed the study of " critical " species is carried on still almost entirely 



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