Genetic Factors 



447 



ternally and internally. In some the cells in certain tissues were larger 

 and in some smaller than in the diploid. Such traits as the size of the 

 bundles, the amount of internal phloem, and the development of peri- 

 cycle fibers differed among the mutants. It is significant that for each 

 trait the diploid was approximately the average of the 12 mutants, a good 



2N 



i-i- 



I 2- 



22- 



3 3 



— 3-4 



5-5- 

 5 6 — 



77- 



II II 



1112 — 



1313 



13-14 



14 14-- 



15-15- 

 15 16- 



17 17 — 



23 24- 



IN- 



6 6 



■7 8 



—910 

 1010 



9 3 



■1718 



19-19 



19-20 



•21-22 



2 N 



■3N 



■4W 



210 2.58 3.06 3.54 4 02 451 5.00 



Fig. 19-18. Genie balance in Datura stramonium. Cross-sectional area of flower stalk 

 in various chromosomal types (in square millimeters). Vertical line marks normal 

 value for the diploid. Areas larger or smaller than this are shown by the lengths of the 

 horizontal lines for each type. IN, 3N, and 4N are below. Above, the primary mutants 

 have solid lines, the secondaries dotted ones. Each chromosome is numbered by its 

 two ends, the primaries being 1.2, 3.4, etc., and the secondaries 2.2, 3.3, etc. The 

 geometrical mean of the primaries is almost exactly the value for the diploid. (From 

 Sinnott, Houghtaling, and Blakeslee. ) 



example of genie balance (Fig. 19-18). Evidently each chromosome 

 contributed something to the character of the plant, and when this 

 chromosome was represented by three instead of two, this contribution 

 was increased. Such a result seems clearly to be due to the genes which 

 the chromosome carries, however, rather than to something specific in 



