6 4 AMERICAN JOURNAL OF BOTANY 



[Vol. 8 



3. An investigation of the correlations between these internal characters 

 (such as those which exist between bundle number in different regions of 

 the seedling) and between the internal characters and external features ol 

 the plant. 



The results of the first and second phases of the investigation are set 

 forth in the present paper; the third is reserved for a later publication. 



MATERIALS AND METHODS 



A priori considerations seemed to indicate that a promising line of 

 attack upon the general field of quantitative plant morphology lay in the] 

 investigation of vascular bundle number. Such an investigation should be 

 on a scale sufficiently large to make possible the determination of trust 

 worthy biometric constants, and should have as its subject a plant organ of 

 relatively simple but variable structure. Because of the ease with which 

 they can be grown in quantity, their sharply marked external characteristics; 

 their convenient size for histological work, and their relatively simple j 

 internal structure, seedlings of Phaseolus vulgaris furnish highly satisfactory] 

 material for a study of variation and correlation in vascular structures. 



Among the many types of variant seedlings of the garden beans which i 

 may be secured by extensive plantings, two were selected for investigation: 

 (a) normal (dimerous] seedlings, with two cotyledons and two primordial 

 leaves, and (b) trimerous seedlings, with three cotyledons and three pri 

 mordial leaves. For brevity in table headings the dimerous plants will? 

 sometimes be represented by &quot;2-2&quot; and the trimerous by &quot;3-3,&quot; where the 

 first figure gives the number of cotyledons and the second the number of 

 primordial leaves. 



Since one of the purposes of this work is to carry out a comparison of 

 bundle number in normal and teratological seedlings, the selection of a 

 satisfactory control series of normal plants is a matter of primary impor 

 tance. It is essential that the seedlings of the types to be compared be 

 selected in a manner to reduce to a minimum any external influences tending 

 to bring about differences between them. It is clear that if the abnormal 

 and the normal seedlings were taken from different series of parent plants, 

 either genetic differences or environmental influences acting upon the parent ~ 

 plant might be effective in bringing about a differentiation in the characters 

 of the seedling examined. A normal seedling from the same parent was, 

 therefore, taken for comparison with each abnormal seedling 1 in each 

 series in which the seed was derived from individual parent plants. Closer, 

 control of the influence of innate differences in the parents and of the possible 

 influence of parental environment hardly seems practicable since the 



1 In the vast majority of the cases one abnormal seedling only was sectioned from a 

 parent plant. When more than one abnormal seedling was available a control was taken 

 for each. Naturally it is immaterial whether control a or b be compared with abnormal 

 seedling A or B, since all are siblings. 



