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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 or 
two in number. At the node the same general procedure is followed as in 
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 ii. 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 18 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., 
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. 
