70 AMERICAN JOURNAL OF BOTANY Vol. 8 



bundles occurring in the upper part of the root (fig. 7). This number is 

 soon reduced to five and eventually to four, in passing down the root. 



Passing upward into the hypocotyl, the six main strands (the primary 

 double bundles) divide to produce twelve (figs. 8 and 9). Intercalary 

 bundles are much less common than in the normal seedlings, appearing in 

 only a small percentage of cases, and then being rarely more than one cm 

 two in number. At the node the same general procedure is followed as im 

 the normal seedling, except, of course, that there are more bundles concerned. 

 Bundles of adjacent pairs approach and fuse (fig. 10). Each of these 

 bundles or bundle aggregates then divides, generally into three. Three 

 cotyledons are each supplied with two bundles (solid black), and three 

 sets of three bundles each each formed by the fusion of two lateral 

 bundles in the intercotyledonary plane remain behind. The bundle 

 changes and the final condition at the departure of the cotyledonary traces 

 are shown in figure 1 1 . The epicotyledonary ring which forms from the 

 bundles which remain thus consists of nine strands instead of the normal 

 six. Many of these divide at once, although the number is not usually 

 doubled, as in normal seedlings, but varies from 12 to 1 8 or even more in 

 the mid-region of the epicotyl (fig. 12). The bundles are much more crowded 

 than in the normal seedlings, which may perhaps account for the failure of 

 some of them to divide at once. 



A study of the first epicotyledonary node shows that three strands are 

 given off to each primary leaf, leaving from 6 to 9 in the stem. 



It is therefore evident that within classes of seedlings which are uniform 

 externally there are considerable anatomical variations and that the two 

 classes investigated are profoundly differentiated in their anatomical organi 

 zation. 



Our next task is to subject the mass of data upon which these general 

 conclusions are based to a statistical analysis with the object of bringing out 

 otherwise undeterminable relationships. 



BUNDLE NUMBER AND ITS VARIATION AT DIFFERENT LEVELS IN THE 



SEEDLINGS 



From the statistical side we have two problems to consider. 



The first is that of the relative numbers of bundles at different levels, i.e. t 

 in the root, at the base of the hypocotyl, in the central region of the hypo 

 cotyl, and in the epicotyl of the same plant in both normal and abnormal 

 plants, together with the variability in bundle number in different regions. 



The second is that of the differences in bundle number, and in variation 

 of bundle number, between normal and abnormal plants. 



Since it is impossible to consider type and variation of bundle number at 

 different levels without noting differences in the trimerous and dimerous 

 forms upon which the observations were based, we shall devote this section 

 primarily to a parallel discussion of both problems. 



