ioi 4 
Journal of Agricultural Research 
Vol. V, No. 22 
stomatal pore lengths 
The stomatal pore lengths of the different types of leaves show varia¬ 
tions that are comparable to those observed in stomatal numbers—i. e., a 
smaller stomatal size must accompany the greater stomatal numbers per 
unit area. The pore lengths (Table II) of the stomata on the heart 
leaves (14/x, upper surface; 14/x, lower surface) are on the average about 
half that of those on the mature leaves (28.5/*, upper, 27.1/*, lower), and 
in turn the mature leaves show a slightly shorter pore length than those 
on the old leaves (31.06/1, upper, and 30.5/1, lower) or cotyledons (31.8/t, 
upper, and 32.1/i, lower), the last two sets being about equal. 
Table II .—Average lengths (in microns ) of stomatal pores on the upper and the lower 
leaf surfaces of heart, mature, and old haves and cotyhdons of the sugar beet. Readings 1 
taken at Madison, Wis., on fuly 6, IQ14. The number of readings made per haf is 
given in parentheses fallowing each average 
1 These leaves were used for the readings given in Tables I, III, and V, and each leaf has the same number 
in all the tables. 
It thus appears that a definite relation exists between stomatal pore 
length and maturity of the leaf, although at times a shorter pore length 
might indicate the maturity as being somewhat less than would be shown 
by the number of stomata present. This may be due to the completed 
growth of the epidermal cells being attained before metabolic activity 
reaches its maximum, and consequently the stomatal pore length would 
be less. 
