Summary. 
5 
clusters appear at about the fifth to the eighth node and the others 
progressively higher as new internodes are added. Growth of the 
axis is terminated only by accident, unfavorable surroundings, 
the drain of seed production, and the like. If favorable conditions 
for growth are provided and if heavy seed production is prevented, 
pole beans can be kept growing for a long time if not indefinitely. 
Plants of both classes grow slowly at first and then increasingly 
more rapidly. In bush beans growth is terminated early in this 
period of acceleration in growth rate. In pole beans acceleration 
in growth rate continues for a considerable time, but retardation 
in growth rate occurs eventually because of the drain of seed 
production, increasingly unfavorable weather conditions late 
in the season, and the like. 
The twining habit common in pole beans is also exhibited by 
the taller bush beans when they are forced into very vigorous 
growth. Its failure to develop in bush beans as a whole is due 
to the fact that growth of the axis is terminated too soon. 
While bush beans are commonly more branched than pole 
beans, there are great differences within both classes with respect 
to this, so that branching habit cannot be used to characterize 
the classes. 
Pole and bush beans also differ in height in consequence of 
the difference in habit of growth. Obviously, height of plants 
depends upon number of internodes and internode length. Bush 
beans have a short axis in part because of a small number of 
internodes and in part also because of a relatively small mean 
internode length, the latter being due to termination of the plant 
axis early in the period of growth-rate acceleration. Pole and 
bush beans, then, are characterized by differences in height, 
only in so far as height is dependent upon determinate and in- 
determinate habits of growth. Races of bush beans differ mater- 
ially in height and the same is true of pole beans. 
Since the axis of a bush bean is terminated early in thei period 
of growth-rate acceleration, its actual internode length s con- 
siderably less than its potential internode length. The latter 
can be determined only by crossing the bush bean with a pole 
bean and by comparing the internode length of the plants of 
indeterminate growth habit thus produced with that of the pole- 
bean parent or by comparing both with some other pole bean 
used as a standard. 
The F2 pole-bean segregates of such crosses are better for this 
purpose than the Fi plants, because increased vigor due to heter- 
ozygosis is much less in F2 than in Fi. By comparing the potential 
internode lengths of bush beans, as determined by this method, 
with the actual internode lengths of these bush beans, it is found 
