338 
T. H. GOODSPEED AND R. E. CLAUSEN 
in the case of the means for 75 plants of N. Tabacum var. macrophylla 
(U. C. B. G. 22/07) is 26.83 ± -09 mm., and the range of fluctuation 
is 7 mm., from 25 to 31 mm. On the other hand, the total range in 
corolla spread as shown by the complete records amounted to 18 mm., 
from 18 to 35 mm.; and for individual plants as high as 14 mm. 
Similarly for length of corolla tube, as shown in Table Ih, the mean 
was 44.27 zb .07 mm. with a range of fluctuation of 7 mm., from 41 to 
47 mm. The complete records, again, show a total range of 18 mm., 
from 33 to 50 mm., for length of corolla tube. These facts are based 
upon measurements continued for nearly one month or in a few cases 
for over one month of the blooming period normal for this species 
and variety. If now the mean flower size is determined on the basis 
of measurements taken during the first 3 or 4 days of this period, the 
mean spread of corolla is 28.48 =b .09 mm., as contrasted with 26.83 =1= 
.09 mm., and the length of corolla is 45.60 db .07 mm. as contrasted with 
44.27 zb .07 mm. Similarly if the mean is determined by measure- 
ments taken on all the plants at the end of this period, the mean 
corolla spread is 24.19 zb .22 mm. as compared with the mean for 
totals of 26.83 =i= -09 mm. and the mean for the first dates of 28.48 
zb .09 mm. In the same way for the length of corolla we have a mean 
of 42.25 zb .15 mm. at the end of the season, while the mean for 
totals is 44.27 zb .07 mm., and the mean at the beginning of the 
season is 45.60 zb .07 mm. If in the third place the mean is derived 
by measuring flowers on the first third of the plants early in the 
season, on the second third in the middle of the flowering season, and 
on the remainder of the plants toward the end of the season, we have 
for spread a mean of 26.69 =t -20 mm. which, as would be expected, 
is practically the same as the mean for totals 26.83 =t -09 mm., but 
differs from the means for the first and last dates which are 28.48 zb .09 
mm. and 24.19 zb .22 mm., respectively. Similarly with reference to 
length of corolla we have a mean of 43.96 zb .18 mm. for such a dis- 
tribution which is very close to the mean for totals of 44.27 dz .07 mm., 
but is distinct from the means of the first or last dates which are 
45.60 zb .07 mm. and 42.25 zb .15 mm., respectively. The amount of 
these differences and their probable errors are tabulated in Table 6, 
where they may be compared with similar differences shown in other 
series of plants. 
The differences between the means according to different times of 
measurement and different modes of arrangement furnish the basis for 
