VOL. 7, 1921 



BOTANY: HARRIS AND SINNOTT 



37 



and trimerous seedlings is conspicuously shown by the frequency distri 

 butions of two of the lines shown in diagram 1 . 



In passing upward from the base of the hypocotyl, each primary bundle 

 pair normally divides into two so that in the central region of the hypocotyl 

 the bundle number is normally twice the number of primary double bundles 

 at the base, plus the intercalary bundles. In many cases the number is 

 somewhat in excess of this, however, showing either that new (intercalary) 

 bundles have appeared or that some of the bundles have become sub 

 divided. 



The modal number of bundles in the mid-region of the hypocotyl is 

 eight or ten in dimerous plantlets; in trimerous and hemitrimerous plantlets 



10 II 12 13 14 IS IB 17 



DIAGRAM 1 



Percentage frequency distributions of total bundles (primary double bundles counted 



as two^l at the base of the hypocotyl in dimerous and trimerous seedlings 



of two lines. Abscissae represent bundle numbers, ordinates 



represent percentage frequencies. 



it is twelve. On the average the number is from 1.7 to 3.8 bundles higher 

 (or from 15.7 to 47.9% higher) in the trimerous than in the dimerous 

 seedlings. The differentiation of the two classes of seedlings in their 

 vascular anatomy at the level is clearly shown in diagram 2. 



The bundles in the mid-region of the epicotyl show in dimerous plantlets 

 a modal number of twelve, whereas in trimerous seedlings it is fifteen. 

 On the average there are from 2.8 to 3.7, or from 23.0 to 30.2%, more 

 bundles in the epicotyl of the trimerous than in the dimerous seedling. 



