308 BOTANICAL GAZETTE [MAY 
In 1906, 15 of the constants have the positive and 5 the negative 
sign; in 1907, only one of the 16 is negative. Throughout, the 
values are too low to be of any practical significance. The mean 
for 1906 is 0.0282, and for 1907 it is 0.0658. We have already 
found low values for 7,, and with the very small values for 75, just 
demonstrated, it seems hardly worth while to calculate pj,. But, 
1s — Tiolso 
using the formula p);= 
: 7 , and substituting the 
V1] Vito 
mean values of the constants for the individuals as the most trust- 
worthy measures for the physiologist, we find: 
Relationship 1906—20 shrubs |1907—16 shrubs 
PAVORROE Pig oon ee ee ee 0.1282 0.1240 
ANGEABE Fo is oe Ls Ses ot 0.0282 0.0658 
NECA Vig Ges wees eta 0.3868 0.3636 
RAICUIRIOG Pig 6c fice se cess 0. 3865 0.3591 
Tis —Pis Oia Re ar Re ae ee 0.0003 0.0045 
Obviously there is no practical significance whatever to be 
attached to the differences such as 0.0003 and 0.0045. In Cercts, 
7; is very materially reduced when allowance is made for the 
influence of the number of ovules. The two foregoing methods 
show that in Staphylea r,, is essentially independent of 7. and 750. 
2. THE HYPOTHESIS OF MECHANICAL STRETCHING 
Where the seeds in a locule attain a considerable size and are 
numerous, it is quite possible that an increased size of the fruit 
might result from their space requirements, through the purely 
mechanical effects of crowding. In Cercis the seeds are relatively 
small and, generally at least, not in contact. Mechanical stretch- 
ing seemed almost entirely excluded by the nature of the material, 
and I gave no attention to it. In Staphylea there seems even less 
reason to suppose this factor to be of any importance, but it is well to 
have such conclusions based on actual statistics. To test whether 
there is a sensible influence of the spatial requirements of the seeds 
upon the length of the pods, I think we may proceed as follows. 
Clearly there can be little mechanical stretching of the placental 
space due to the development of a single seed in a locule. All the 
