^ A Genetic Study of Plant Height in Phaseolus Vulgaris. 19 
have arisen as a mutation from pole Limas (Bailey 1895) and, 
since bush Limas bear the same relation to pole Limas as bush 
forms of the common bean do to the common pole beans, it seems 
probable that the common bush bean is a mutation from the 
pole bean. If this is true, the terminal inflorescence of bush 
beans may be regarded as a direct modification of the main axis 
of pole beans in which the leaves are reduced to mere bracts and 
in which the axis does not elongate indefinitely. The order of 
development of the flowers in the terminal inflorescence of bush 
beans remains exactly like the order of development of the 
flower clusters along the main axis of pole beans. 
In this connection, attention should be called to the fact that, 
w^hile the axillary flower clusters of some pole beans usually 
consist of but two or three flowers, like the individual flower 
clusters of the terminal inflorescence of bush beans, many var- 
ieties of pole beans have an axillary inflorescence identical with 
the terminal inflorescence of bush beans rather than with the 
individual flower clusters of that inflorescence. Such a condition 
is shown in Figure YD, where a small part of the main axis of the 
plant is seen at the right and parts of a leaf and petiole at the 
left. It is conceivable that bush beans arose from pole beans 
thru the failure of the main axis to develop beyond a certain node. 
In this case an axillary inflorescence of the pole bean would become 
the terminal inflorescence of the bush bean. On this supposition, 
however, one could hardly explain the presence of the flower 
cluster almost, if not quite, universally seen in the axil of the 
upper leaf of bush beans, as illustrated in Figure 7A. 
Usually the uppermost leaf of bush beans, which is here 
regarded as marking the end of the plant axis proper and the 
beginning of the terminal inflorescence, is at least as large as 
any of the other leaves of the same plants. The plant axis 
maintains its thickness to the upper leaf and there changes 
abruptly to the more slender axis of the terminal inflorescence. 
Sometimes, however, tho this is a rare occurrence, the upper 
leaf is very small and may even consist of only a single leaflet. 
The internode just below such an ill-formed upper leaf is shorter 
and more slender than in ordinary plants, so that the transition 
from plant axis to terminal inflorescence is somewhat gradual. 
Very rarely the axis of a distinctly pole-bean plant terminates 
abruptly in an inflorescence like that of a bush bean. The first 
plant of this sort to attract my attention was one of the small 
pole-bean race known as Snowflake. The plant was grown in a 
small pot of rather poor soil. When two months old, it had 
reached a height of 53 centimeters, formed 17 internodes, pro- 
duced a fair crop of pods, and practically ceased growing. It was 
