64 
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 of 
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 
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 
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 "2-2" and the trimerous by "3-3," 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^ 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 
^ 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 & be compared with abnormal 
seedling A or B, since all are siblings. 
