432 AMERICAN JOURNAL OF BOTANY [Vol. 8. 



This result for seedlings of the same morphological type is suggestive in 

 its relation to the results of a comparison of seedlings which are externally 

 dimerous and trimerous, since in general trimerous seedlings show an increase 

 in number of primary double bundles but a decrease in number of intercalary 

 bundles as compared with dimerous seedlings. As a result of this numerical 

 compensation, most conspicuously evident in the trimerous seedlings, the 

 total number of bundles shows a lower variability than it would if the num 

 bers of the two types of bundles were quite independent. 



2. The correlation between the total number of bundles (primary double 

 bundles plus intercalary bundles) and the number of intercalary bundles is 

 high. The coefficients for the dimerous seedlings are somewhat higher 

 than those for the trimerous seedlings. The correlation between the total 

 number of bundles and the number of primary double bundles is generally 

 much lower. The correlation between the total number of bundles and 

 the deviation of the number of intercalary bundles from that which would 

 be expected if they occurred in the same proportionate frequency throughout 

 the entire range of total bundle number is positive in sign and substantial 

 in magnitude. In both types of seedlings variation in the number of 

 intercalary bundles is therefore an important factor in determining variation 

 in the total number of bundles at the base of the hypocotyl. 



