324 
M. R. ENSIGN 
better method of insuring comparable volumes could be hit upon than by 
taking those cells in the cortex at the same distance from the base of the 
root cap and which contained nuclei that were round in section. The 
volume of the cytoplasm was assumed to be that of the cell minus the volume 
of the nucleus. The volumes were computed on the basis that the cells 
were cylinders, and the nuclei spheres. 
Fourteen root tips from each of the A and B hypocotyls were examined. 
In table 7, these data are summarized. The figures representing the volume 
of nucleus and cytoplasm, respectively, for each root tip, are averages of 
fifteen to twenty-five determinations. 
Ta-BLE 7. Summary of determinations of nucleo-cytoplasmic ratios made from each pair of 
polyembryonic root tips of Citrus grandis 
No. of 
Root Tip. 
Volume Nucle 
(Cu. Microns) 
Volume Cytoplasm (Cu. Microns) 
Nucleo-cytoplasmic 
Ratio 
A 
B 
B 
A 
B 
I 
166.89 
187.05 
626.06 
544-13 
3-9 
I 
: 2.9 
2 
195.02 
187.05 
881.04 
544-13 
4.4 
I 
: 2.9 
3 
166.89 
164.52 
1,168.47 
826.81 
7 
I 
: 5 
4 . 
187.05 
187.05 
1,397-27 
1,265.36 
7 
I 
:6.7 
5 
166.89 
142.03 
1,168.47 
868.23 
7 
I 
: 6.1 
6 
130-58 
187.05 
1,189.14 
1,113.80 
9 
I 
: 5-9 
7 
187.05 
164.52 
778.67 
566.66 
4 
I 
: 3-4 
8 
142.03 
194.99 
687.64 
994-93 
4-8 
I 
: 5 
9 
160.69 
180.75 
1,123-38 
658.11 
7 
I 
: 3-9 
10 
226.18 
191.94 
1,421.63 
672.22 
6 
I 
: 3-9 
II 
180.75 
154.20 
1,428.39 
843.04 
7-9 
I 
: 6 
12 
194.99 
140.26 
686.72 
1,430.70 
3-5 
I 
: 10 
13 
166.97 
157.08 
1,053.67 
1,414.04 
6.3 
I 
: 8 
14 
174-59 
173-19 
1,396.88 
1,267.60 
8 
I 
: 7 
Mean . . . 
174-75 
171.52 
1,069.60 
859-30 
I 
6-3 
: 5.0 
The results show that the nucleo-cytoplasmic ratio as determined by 
this method is subject to considerable variation. This may be explained 
in part by the fact that the percentage of vacuolization of the cytoplasm at 
an equal distance from the apical cell of the meristem is not the same in 
every root tip. It is, obviously, impossible to make the necessary correc- 
tions, for there is no way of knowing the degree of differentiation that has 
taken place. The only possible way to overcome this difficulty is to take 
mean averages of many determinations. The mean averages for fourteen 
root-tips examined show that in a measure this error has been overcome. 
It also shows that the nucleo-cytoplasmic ratio is not appreciably different 
in the A and B root-tips. Certainly the difference is not as great as the 
individual variations in either case. 
Some Physiological Considerations 
Since the two tests which have gone before have revealed no apparent 
difference between the seedlings arising from a single seed, the question 
then naturally arises: Do the polyembryonic seedlings from single seeds 
