SOME NEW CASES OF MENDELIAN INHERITANCE 



GEORGE HARRISON SHULL 



(WITH FOUR FIGURES) 



In crosses between nearly related elementary forms, numerous 

 investigations have shown that a very wide range of characteristics 

 in a great many species of both plants and animals behave in the Men- 

 delian way; that is, they give a uniform progeny in the first hybrid 

 generation (F x ), and show perfect segregation of the various character- 

 istics in F 2 and later generations. So consistent have been the results 

 that there can be no question that MENDEL'S law has fundamental 

 and widespread applicability, but it has also been demonstrated that 

 it has its limitations. Where these limitations lie and why it is thus 

 limited may not be known until a much larger mass of data is on 

 record than is now available. 



Several of the cultures at the Station for Experimental Evolution, 

 upon which no report has yet been published, present new instances 

 of Mendelian heredity under conditions which make their considera- 

 tion desirable, even though only a preliminary account can be given 

 at this time. 



HELIANTHUS ANNUUS L. 



Among 112 plants of the so-called "Russian" sunflower (Heli- 

 anthus annuus var.) grown at the Station during the summer of 1904, 

 all but one had the usually unbranched stem surmounted by a single 

 large head. Sometimes these had several weak branches in the axils 

 of several of the lower leaves, but there were never more than three 

 or four of these lateral branches, and none ever stood higher on the 

 stem than the fifth node above the cotyledons. The one exceptional 

 individual had strong branches in nearly all of the axils and bore a 

 number of somewhat smaller heads, but was not observed to differ in 

 other respects from its unbranched neighbors (figs, i, 2). The seeds 

 had been purchased at a seed store, and nothing is known of the 

 antecedents of these plants. 

 103] [Botanical Gazette, vol. 45 



