62. TENOPYR: CONSTANCY OF CELL SHAPE 
smallest squares of the ocular micrometer. The number of cells 
cut by each side of the square was counted. The length of this 
line was then divided by the cell number to obtain the average cell 
diameter. In this way, with one placing of the micrometer, I 
could make four measurements, two giving the length and two 
giving the width of the palisade cells of the region. 
To measure the epidermal cells, a suitable area, free from veins, 
was selected. To avoid errors due to the presence of stomata, 
care was taken in each case to so place the micrometer that the 
stomata came between but not on the lines of measurement. In 
plants having numerous stomata, this was often a difficult matter. 
In this case I used twice as large a micrometer unit, the sides of 
two squares, corresponding roughly to the larger size of the cells. 
CAMPANULA ROTUNDIFOLIA 
Campanula rotundifolia is well known as a plant whose radical 
and cauline leaves differ widely in shape. It produces numerous 
radical leaves, which are often wanting at the time of flowering. 
These are petioled, almost orbicular in shape, with cordate base. 
In May or June the plant sends up several shoots which bear 
flowers at their summits throughout thesummer. The upper stem 
leaves are sessile and linear, but the lower stem leaves are inter- 
mediate in shape, being ovate and acute. These three types of 
leaves are designated in the tables as basal, transitional, and linear. 
Measurements were made of the length and the width of the 
cells of the lower epidermis of typical leaves of the three forms 
described. TABLE I gives the results of these measurements. 
The average number of cells in each leaf that were cut by a line 
I mm. in length, is given for each of six leaves of each shape. The 
final averages are from the original data and differ fractionally 
from the average of the averages in the following table. 
A comparison of the average number of cells to 1 mm. found 
in the long and the broad axis of each basal leaf shows that there 
is some variation in the size of the cells, for example, in leaf C the 
average number being 22.02 cells to 1 mm. in the long axis and 20.91 
cells in the transverse axis, while in leaf D the cell counts were 
26.95 cells in the long axis and 29.56 cells in the transverse axis of 
the leaf. These figures also serve as an example of the variability, 
