78 AMERICAN JOURNAL OF BOTANY [Vol. | 



from 60 to 78 percent smaller in the trimerous than in the dimerous seedlings. 



In line 139 the mean number of intercalary bundles is actually larger 

 in the trimerous seedlings, but the difference is only +-O2 .02. 



In line 143 the mean number of intercalary bundles in trimerous and 

 dimerous seedlings is practically identical, the difference being only .02 

 .03. In both of these lines the differences are insignificant in comparison 

 with their probable errors. 



It is also interesting to note that in lines 75, 93, and 98 the differentia 

 tion between abnormal and normal seedlings is greater with respect to the 

 number of intercalary bundles than with respect to primary double bundles. 

 Turning back to table 4, we note that the number of primary double bundles 

 is from 31 to 44 percent higher in the trimerous plants, whereas the number 

 of intercalary bundles is from 60 to 78 percent lower. In lines 139 and 143 

 the difference in the mean of the number of primary double bundles of 

 trimerous and dimerous plants is practically the same as in the other lines, 

 but in these lines the two types of seedlings are essentially identical in 

 number of intercalary bundles. 



If we consider the comparative variability of dimerous and trimerous 

 seedlings as to intercalary bundle number, we find that here, as in the case 

 of number of primary double bundles, the lines differ among themselves. 

 In all lines except 139 the standard deviations of number of intercalary 

 bundles in the trimerous seedlings are smaller than in the dimerous. In 

 lines 75, 93, and 98 the constants for the trimerous seedlings are from 33 to 

 38 percent smaller than those of the dimerous controls. In line 143 the 

 difference has the same sign but is only 9.38 percent of the control value. 

 In line 139 the difference is -}- n.88 percent. 



The coefficients of variation are very high in both normal and abnormal 

 seedlings, and this great variation renders the probable errors of little value 

 as criteria of statistical significance of differences between the two types 

 of seedlings. In lines 75, 93, and 98, the coefficients of variation for tri 

 merous plants are conspicuously higher than those for the dimerous controls. 

 In line 143 the coefficients of variation for the two types of seedlings are 

 practically the same. In line 139, however, the coefficient of variation for 

 the number of intercalary bundles is higher in dimerous than in trimerous 

 plants. 



C. Total Bundles. Having considered the frequency distribution and 

 statistical constants for the two types of vascular structures found in the 

 base of the hypocotyl, it is now desirable to combine the two types of bundles 

 in order to consider the total number of vascular elements at this level. 



This problem presents certain morphological difficulties. The primary 

 double bundles are each derived from a single root pole, and do not become 

 clearly divided into two bundles until the level of transition is reached from 

 root structure to stem structure at the base of the hypocotyl. Many of 

 the intercalary bundles appear at this level or a little lower. In determining 



