HARRIS: INTERRELATIONSHIP IN PHASEOLUS 169 



seed flat were potted side by side in a three inch pot and allowed to 

 grow to the proper stage of maturity under conditions as favorable 

 as we were able to give them. 



Before the samples were taken, the plants were carefully inspected 

 and all pairs, one member of which had died, had been injured or 

 which showed in its subsequent development any abnormality in addi- 

 tion to these specified were discarded. Note that there was no direct 

 selection for the characters of the abnormal plantlets in this process, 

 since both abnormal and control were discarded if either was unsuited 

 for the purposes of the experiment. 



There probably was a fairly stringent indirect selection, since the 

 death rate and the mutilation rate of the variant individuals was 

 probably greater than that of the normals. Thus more pairs were 

 probably discarded because of an injury to or the death of the ab- 

 normal member of the pair than because of the death or injury of a 

 normal member. 



The probability that the materials were somewhat selected before 

 the physiological measurements discussed in this paper were carried 

 out renders the findings of greater significance than they would 

 otherwise be. 



After the pairs of seedlings had grown until the first compound 

 leaf had attained its full size, and the second compound leaf was 

 developing, but before the primordial leaves had materially deteri- 

 orated, samples of leaves were taken by nipping off the laminae only, 

 or the laminae and the single petiolule of the terminal leaflet in the 

 case of the compound leaf. These samples of tJssues,_ea(:li_ from 

 loo^pla nts, w ere enclosed in flasks, wei^hed^ and dr ied to constant 

 weight in a bath surrounded by boiling water. 



Thus the. technique employed was exceedingly simple. Because 

 of the size of the samples dealt with, the relative infrequency of the 

 abnormalities, and the large number which had to be discarded, the 

 routine has been excessively laborious. For example, the weighings 

 of the 23 samples and checks discussed in the present paper involve 

 13,800 leaves gathered from 4,600 plants which were secured by 

 germinating and classifying nearly half a million seedlings. 



The structural variation in the bean seedling which is probably the 

 simplest, and the most frequent, is a slight vertical separation of the 

 cotyledons which are normally sensibly opposite in insertion. The 

 amount of the separation is difficult to express quantitatively, since 

 it is in some degree dependent upon the length of the axis. In our 

 studies of seedling variation in Phaseolus, three grades of separation 

 of the 'cotyledons have been recognized. The line of demarcation 

 between these grades is a quite arbitrary one. This is also true of 



