A Genetic Study of Plant Height in Phaseolus Vulgaris. 43 
That the potential internode length of Triumph is considerably 
less than that of Red Marrow, as was earlier indicated by direct 
comparison of the first five internodes of these bush races by which 
a mean-length ratio of 100:58 was indicated, is shown by a com- 
parison between the Red Marrow-Snowflake and Triumph- 
Snowflake crosses, between these crosses and Snowflake, and 
between them and the July-Snowflake cross. The internode 
length of the Triumph-Snowflake cross was 81 per cent of that 
of Snowflake which was only 86 per cent of that of the Red 
Marrow-Snowflake cross. Again the internode length of the 
Triumph-Snowflake cross was .57 per cent and that of the Red 
Marrow-Snowflake cross 82 per cent of the internode length of 
the July-Snowflake cross. From either of these comparisons, 
it follows that the internode length of the Triumph-Snowflake 
cross is 70 per cent of that of the Red Marrow-Snowflake cross, 
and this is also shown by the direct comparison of these crosses. 
That this difference between the Red Marrow-Snowflake and 
Triumph-Snowflake crosses, as determined from the first 15 
internodes, is much less than the difference between Red Marrow 
and Triumph, as determined from the first five internodes, is 
not to be taken as an indication that differences in potential 
internode length of bush beans are not suggested even roughly 
by direct comparison. That the difference between the crosses 
was less than the difference between the races themselves was to 
have been expected, since Snowflake was intermediate between 
the bush races in internode length and should, therefore, produce 
crosses with these races having internodes shorter than those of 
Red Marrow and longer than those of Triumph. If the Red 
Marrow-Snowflake cross were exactly intermediate between Red 
Marrow and Snowflake and the Triumph-Snowflake cross exactly 
intermediate between Triumph and Snowflake, the difference 
between the two crosses should be one-half the difference between 
Red Marrow and Triumph. The difference between the crosses 
was 30 per cent of the larger cross (100 — 70) and the difference 
between the bush races was 42 per cent of the larger race (100 — 
58). The difference between 30 per cent and 21 per cent (one- 
half of 42 per cent) seems a fair measure of the accuracy with 
which differences in potential internode length of bush beans can 
be judged from a comparison of the actual internode lengths of 
the bush beans themselves. 
The foregoing comparisons, as a whole, indicate that the po- 
tential internode lengths of bush beans can be determined roughly 
from measurements of the first five internodes. The length of 
the first 15 internodes is thought to give a fair approximation 
