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. 
