46 



THE AMERICAN NATURALIST 



[Vol. XLIX 



has now been done for twenty series of pods, drawn from five 

 cultures belonging to three distinct varieties (Navy, Golden Wax 

 and Burpee's Stringless) and embracing altogether about 23,000 

 individually weighed seeds. In every one of these cases a positive 

 correlation has been found, i.e., the weight of the seed increases 

 as its distance from the base of the pod becomes greater. The 

 intensity of this interdependence is, however, not very great, at 

 least in the varieties so far studied. The correlations range from 

 .014 ± .046 to .238 ± .068, with an average value of about .132, 

 or about 13 per cent, of perfect correlation. 



The rate of change has been expressed by the slope of a straight 

 line for four different classes of pods studied for a culture of 

 Navy beans made at Sharpsburg, Ohio, in 1907 (Diagram l 3 ) and 

 for five classes from a culture of Burpee 's Stringless beans grown 

 at the Missouri Botanical Garden in the same year. 



In the first of these, the 

 Navy series, it appears that 

 the observed mean weights at 

 first increase rather rapidly, 

 then the rate of increase falls 

 olf and finally the seeds near- 

 est the tip (distal or "blos- 

 som" end of the pod) become 

 somewhat lighter than those 

 a little lower down. Here a 

 curve would fit the observed 

 means better than a straight 

 line. In the Burpee's String- 

 less culture (Fig. 2) however, 

 the change in seed weight can 

 for all practical purposes be 

 represented by a straight line 

 as well as by any curve. 



The percentage of ovules 

 which develop into seeds also 

 increases from the base to- 

 ward the stigmatic end of the 

 pod. In small pods the rate 

 of increase may be fairly 

 regular, but in larger pods 



eries published in the original paper there is a 

 the slope of the line for pods with 4 ovules. 



























































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