376 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
tions which furnished the materials for our earher discussion of dimerous 
and trimerous seedHngs. The dimerous and hemitrimerous seedlings were 
derived from the same parent plants in lines 75, 93, and 98. In lines 29, 
139, and 143 the germinations were made from mass seed instead of from 
the seed of individual parent plants. All of the seed, however, was grown 
in the same experimental field in 191 7. 
Since it has been shown in an earlier paper- that there is practically no 
correlation between the anatomical characters of the trimerous and dimerous 
seedlings from the same parent plant, we are fully justified in using random 
samples of hemitrimerous. trimerous, and dimerous seedlings for a com- 
parison of their vascular characters. 
A detailed account of the vascular topography of the dimerous and 
trimerous seedling is presented in a previous paper by the writers, but may 
be summarized very briefly here. Each primary polar bundle of the root 
bifurcates in the base of the hypocotyl to form a "primary double bundle," 
which gives rise to two distinct and well separated strands in the central 
region of the hypocotyl. In addition to these, there are usually present 
in the hypocotyl a number of "intercalary" bundles, arising either de novo 
or by splitting of some of the primary strands. At the cotyledonary node 
a rather complex vascular anastomosis takes place, from which the coty- 
ledonary strands depart and out of which the vascular system of the epicotyl 
is organized. 
Presentation and Analysis of Statistical Data 
Base of Hypocotyl 
The frequency distribution of the various types of vascular organization 
at the base of the hypocotyl is shown for all the available data in table i. 
In this table the number of primary double bundles appears in parentheses, 
while the number of intercalary bundles follows the + sign. 
Because of the relatively small numbers of hemitrimerous seedlings 
which can be obtained and because of the irregularity of the frequency 
distributions for bundle number, it has not seemed desirable in this paper 
to consider the frequency distributions of the numbers of bundles of the 
several types. Neither has it seemed desirable, on the basis of the rela- 
tively small series of hemitrimerous seedlings which can be obtained, to 
consider the relative variabilities of bundle number in the different regions 
of the three types of seedlings as we did in our discussion of variation in the 
dimerous and trimerous types. We have, therefore, limited ourselves to a 
comparison of mean bundle number, leaving the question of variability 
until larger series of countings can be obtained. 
2 Harris, J. Arthur, Sinnott, E. W., Pennypacker, J. Y., and Durham, G. B. Correla- 
tions between anatomical characters in the seedling of Phaseolus vulgaris. Amer. Jour. Bot. 
8: 339-365. 192 1. 
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