462 THE AMERICAN NATURALIST [Vol. LVI 



Three plants of normal stature were self-pollinated and 

 three -were back-crossed on the double recessive (adherent- 

 brachytic). The six ears were planted separately at Arlington, 

 Virginia, but the resulting F„ populations were not as large as 

 could be desired. 



The combined self-pollinated progenies gave the following 

 distribution : 



Ad. I Br.- Ad. 



These distributions clearly indicate that crossing over between 

 these two factors occurred in from 20 to 30 per cent, of the 

 gametes. 



Additional evidence of linkage between these characters is 

 afforded by the second generation of a cross between an ad- 

 herent plant of normal stature and a ramose-brachytic plant. 

 The F, of this cross was normal with respect to all three char- 

 acters, and they all reappeared in the progenies of the second 

 generation. Five F, plants were self -pollinated and the result- 

 ing ears planted separately. Unfortunately in most of the Fn 

 progenies there is a deficiency of adherent plants and for the 

 combined progenies the departure below the expected 25 per 

 cent, is 7.8 ± .87, a deviation too large to be ascribed to chance. 

 Whether this deficiency represents seedling mortality is not 

 known, but at the time the plants were classified many of the 

 progenies contained late plants strikingly smaller and weaker 

 than their mature sisters. Some of these plants consisted of a 

 small cluster of grasslike leaves with inflorescences hardly de- 

 veloped beyond the embryonic stage. Such plants could not be 

 classified with respect to adherence, though in many cases it 

 was possible to determine satisfactorily whether they were ra- 

 mose or brachytic. With respect to these last two characters 



