THE CAMBIUM AND ITS DERIVATIVE TISSUES 
419 
zoologists indicate that, although in general large cells tend to have larger 
nuclei than small ones, the nucleo-cytoplasmic ratio fluctuates within 
rather wide limits, not only in different organisms, but also during different 
stages in ontogeny and under different environmental conditions. Highly 
specialized tissue cells tend to have very different ratios from those char- 
acteristic of undifferentiated or embryonic elements. 
Table i. Pinus Strohus L. 
Nucleus 
Cell 
Ratio Between 
Volume of Nu- 
cleus and Vol- 
ume of Cell 
Dimensions 
Approxi- 
Volume 
Dimensions 
Approximate 
Volume 
VD 1 RD 
TD 
VD RD 
TD 
Cambium from i -year-old stem 
Ray initials 
Large initials 
63 
77iicrons 
8.7 
3-2 
jnicrons 
6.5 
5-8 
cti. mic. 
350 
1,000 
microns 
22.9 
870 
microns 
17.8 
4-3 
microns 
13-8 
16. 
CU. mic. 
5,000 
60,000 
1:14 
1 : 60 
Cambium from 60-year-old stem 
Ray initials 
Large initials 
12.4 
82 
12.5 
5-9 
9.9 
8.9 
850 
3,500 
24.8 
4,000 
26.6 
6.2 
17.0 
42.4 
10,000 
1,000,000 
1 : 12 
1:286 
Basis: dimensions of cells and nuclei are averages of 50 measurements. 
The cambial initials of arborescent dicotyledons contain smaller nuclei 
(figs. 26, 40, 47) than do homologous cells of gymnosperms (figs, i, 10, 33, 
39, 42, 53), Whether this difference is due entirely to the fact that the 
cambial initials are smaller in the former than in the latter group of plants 
is a question which must be reserved for discussion in a subsequent paper. 
In Coniferae, as illustrated by Pinus Strohus L., the dimensions and volume 
of the nuclei vary considerably in cambial initials of different shapes and 
sizes. The large, fusiform initials have larger and more elongated nuclei 
than the small, roughly isodiametric, ray initials (figs, i, 10, 14, and table i). 
Furthermore, the large cambial initials of stout, mature stems tend to 
contain larger nuclei than do the small, meristematic cells of young shoots 
(table i). However, as shown in table 2, the nuclei of fusiform initials are 
subject to variations in their longitudinal dimensions (VD) which are not 
closely correlated with fluctuations in the length of the cells. The most 
striking of these variations are seasonal. In the stem of the white pine, 
the "resting" nuclei of the fusiform initials tend to be much longer and 
narrower during the fall and winter than during the spring and summer 
(figs. I, 10, and table 2). This change, if it occurs, is much less conspicuous 
in the root (fig. 33). It should be noted, in addition, that the variations 
in the shape of the nuclei are not paralleled necessarily by similar fluctua- 
tions in their volume. This is due to the fact that the changes in length 
