., 1921] HARRIS AND OTHERS SEEDLINGS OF PHASEOLUS 99 



entered it from the hypocotyl. 11 Immediately above the cotyledons 



: s.ix remaining bundles approach, closing the cotyledonary gaps and form- 

 a ring, the six members of which almost immediately divide, giving rise 

 b ! the modal number, 12, which persists throughout the length of the 

 ticotyl. It is apparently the disappearance of the intercalary bundles as a 

 :aspicuous feature of the topography which results in the lowered variabil- 

 \r of bundle number in the epicotyl as compared with the hypocotyl. 



If this conclusion be true, we should find the least difference in the 

 mability of number of bundles in the central regions of the first two inter- 

 ;des in the lines in which intercalary bundles are least conspicuous as a 

 : *ture of the vascular topography. As a matter of fact, this condition is 

 i ongly supported by the results for the five lines investigated. Turning 

 :ck to table 6, showing the constants for number of intercalary bundles, 

 K note that lines 75, ^93, and 98 have on the average from 0.60 to 0.83 

 :ercalary bundle per (normal) plant. These are the lines showing a 

 vative difference of 55 to 65 percent in the standard deviations as com 

 bed with 36 percent in line 143 with an average of 0.31 intercalary bundle, 

 id of only 0.73 percent for line 139 which has an average of only 0.07 

 iercalary bundle per plant. The differences in the coefficients of variation 

 V hypocotyl and epicotyl are from 9.3 to 11.4 percent in the three lines 

 ;th from 0.6 to 0.8 intercalary bundle per plant, 7.5 percent in line 143 

 ;th an average of 0.31 intercalary bundle, and only 1.7 percent in line 

 19 with an average of only 0.07 intercalary bundle. 



In the trimerous seedlings the relationship between the variation of the 

 imber of bundles in the hypocotyl and in the epicotyl is just the reverse of 

 :at found in the normal type. Variability as measured by the standard 

 viation is significantly higher in the epicotyl of all lines studied. The 

 me is true if the coefficient of variation be used as a measure of variability, 

 though the differences for lines 75 and 143 are not large. 



The anatomical explanation of this fact seems to be found in the pecu- 

 irities of behavior at the cotyledonary node. As pointed out above 

 &amp;gt;. 70), the epicotyledonary ring is typically made up of nine strands 

 stead of the six characteristic of the normal plant. There is, therefore, 

 : the modal case an increase of fifty percent in the number of bundles in 

 e epicotyledonary ring of the trimerous plant as compared with the 

 merous plant. Many of these bundles, but not all, divide to form the 

 indie system characteristic of the main course of the epicotyl. It is this 

 inability in the extent of division of the bundles of the epicotyledonary 

 ng which, in connection with the low variability of the hypocotyl due to 

 ie formation of but few intercalary bundles (except in lines 139 and 143, 

 here the number is about the same in normal and abnormal seedlings), 

 &quot;ings about the great variability in the bundle number of the mid-region 



11 This statement is based on a more detailed anatomical study of a portion of the 

 idlings. 



