68 TENOPYR: CONSTANCY OF CELL SHAPE 
longer than those of the round leaves. That is, the difference in 
these two leaf shapes is almost forty times as great as the difference 
in the shapes of the cells. Furthermore, the transitional leaves 
have proportionately wider cells than the basal leaves. 
There is a considerable range of variability in the shape of the 
cells of any one type of leaf. For example, in a basal leaf, D, 33 
mm. long by 30 mm. wide, the average length of the cells of the 
lower epidermis was 0.094 mm., the average width 0.068 mm., 
while in another leaf, G, 50 mm. by 31 mm., the average cell 
measurements were 0.06 mm. for the length and 0.079 mm. for the 
width. The great range of variability of the cell shape of each 
type of leaf may account for the slight difference between the 
ratios of the cell dimensions of the round, the narrow and the tran- 
sitional leaves. 
The decrease in cell size, that is, in both length and width, 
found in the linear leaves as compared with the basal leaves, is 
even more marked than in Campanula rotundifolia. The ratios 
between the corresponding dimensions of the cells of the three 
forms of leaves are given in TABLE V. It will be seen that the 
TABLE V 
LOBELIA ERINUS 
Relative size of the cells of the lower epidermis of the three types of leaves. 
Length of Width of 
cells cells 
Transitional leaf : Basal leaf..... oat 07 21 
Narrow leaf : Basal leaf......... 07.7 OO 2% 
cells of the transitional and linear leaves, both of which grow 
on the stem and are produced at almost the same stage of de- 
velopment of the plants, have cells which are almost identical 
in size, although differing considerably from those of the earlier, 
radical leaves. 
PLANTAGO MAJOR AND PLANTAGO LANCEOLATA 
The leaves of the two species of plantain, Plantago major and 
_ P. lanceolata, differ greatly in shape. The largest and best de- 
veloped leaves of each species that could be obtained, were chosen 
for comparison. P. lanceolata, when crowded, produces leaves 
which are somewhat dwarfed, particularly in their breadth, being 
