20 



Structural Characters : Plants 



[CH. 



often exists in two forms, hairy and glabrous, growing side by side, and 

 doubtless their genetic relations are the same as those found for the. 

 corresponding varieties of Lychnis. In this species a third form is found 

 with hairs on the edges only (12). 



The case of Matthiola is important and presents features of special 

 interest, R.E.C. (19, 20, 21, see also Correns, 61). Between thoroughly 

 hoary and glabrous strains the discontinuity is absolute, and the glabrous 



Fig. 4. Mafthiola, Branched and unbranched forms in F^. A photo- 

 graph of Miss Saunders' plants, the leaves removed. (Supplied by 

 Miss Killby.) 



are entirely destitute of hairs. The dominance is complete and homo- 

 zygotes cannot be distinguished from heterozygotes. A third, or "half 

 hoary" form exists, which is glabrous or nearly so on the upper surface 

 only. Its behaviour has not been fully investigated (19, p. 33.) 



The genetics of hairiness in wheat have been studied by Spillman (247), 

 I'schermak (270), Biffen (27). The heterozygotes are sometimes inter- 

 mediate in hairiness. 



The Peach and the Nectarine are probably related to each other as 

 hairy dominant and glabrous recessive. 



Peculiar results are recorded in Cotton (Balls, 6). 



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