1887] Botany. 18r 
apparently empty and lifeless, but the great majority contained 
nuclei me of these cells must have been quite old, as I ex 
amined some sections s prike from the body of a tree about 
eight inches in diamete 
{n studying the acti of the nucleus and the process of 
cell-division, I had about equal success in the three above-men- 
tioned tissues. 
ig. 4 is from a drawing of a cross-section of a young shoot 
cut April 26, showing a few cells of the xylem (x), the newly- 
formed tissue (7), some cells of the old phlceum (2), and a medul- 
Wid ray (m). In this shoot a zone about seven cells broad had 
med. 
"To obtain some idea of the rate of cell-division I made an 
estimate of the number of newly-formed cells produced by the 
cambium in a piece of a three-year-old stem one inch long, cut 
April 26, by counting the number of cells in the breadth of the 
zone, the number of cells around the stem, measuring the length 
of a number of cells, and taking the eeoa Also, in obtaining 
the number of cells around the stem, I took four sections from 
- different stems, but all of about average size, and took the aver- 
age. By this means I estimated the number of newly-formed 
cells, in such a piece of stem one inch long, April 26, to be 
560,640. As April 17 there were no signs of growth, and as I 
could find but few nuclei and cells in the process of division in 
the material cut April 26, and from the great number of newly- 
formed cells, I conclude that the entire process of cell-division 
can last but a very short time,—perhaps two or three hours. 
Fig. 5, a, ġ, c, d, and Fig. 6, f, g, and Å, are camera drawings 
of some of the forms of the dividing nucleus found in the medul- 
lary rays along the line of the cambium. These are all from a 
four years’ growth, cut May 6 and 
Fig. 6, 7, and Fig. 3, 4, c, d, represent some forms found in the 
cambium from material the same as the above. Fig. 7 represents 
cells from the inner cortex of a young shoot cut May 6, and Fig. 
8, the same from the outer cortex. 
Forms essentially like all these drawn were found in each of 
the three tissues, and from these we can trace the process of 
growth of cell-division in the pine. 
First the nucleus in a state of repose; the nuclear filament 
making the section. It demonstrates the composition of the 
nucleus. About the first change manifest in division is the seg- 
-mentation of the nuclear filament, shown in Fig. 5, c and d. 
Then these segments double and arrange themselves in a radial 
manner around a common centre, as shown in somewhat varying 
stages in Fig. 8, c, and Fig. 6, g and h. Then the oe of 
