498 
WALTER L. C. MUENSCHER 
the other hand, I noticed that for similar areas of the various leaves 
examined the number of stomata was more or less constant for the 
species. I tried to take the upper and lower counts for each leaf 
from similar or corresponding areas. 
The number of stomata per square millimeter varies from an aver- 
age of a maximum of 250 in Phaseolus vulgaris to a minimum of 21 
in Triticum sativum for the lower surface and from a maximum of 71 
in Helianthus annuus to a minimum of zero in Primula sinensis on 
the upper leaf surface. (See Table IV.) 
In Table IV I recorded the minimum, mean, average, and maxi- 
mum number of stomata determined per square millimeter for each 
species. The average number in each case represents the average of 
thirty or more single counts. The minimum and maximum are 
rather widely separated but the mean and average are nearly always 
equal or nearly so. 
These figures do not compare exactly with any figures found for 
the same species by Weiss (13), or Eckerson (5), but the differences 
are not so large but what they may be accounted for by differences in 
conditions under which the plants were grown, or different varieties 
or strains might have been employed by the different investigators. 
In Impatiens sultani I found 29 stomata per square millimeter 
on the upper leaf surface while Eckerson reported that no stomata 
were found by her on the upper leaf surface of the same species. Prob- 
ably I used a different variety of Impatiens sultani. The table also 
shows two sets of figures for Pelargonium zonale, number I was used 
in the first series and number II was used in the second series. These 
are two different varieties, the former has fewer and much larger 
stomata than the latter variety. 
Table V records the size of the stomata for the upper and lower 
surface for the various species. The length and breadth of the 
guard cells and of the pore is recorded in microns. Each number 
represents the average of thirty or more measurements. I found that 
all the stomata as well as their pores were more or less elliptical. 
The length of the pore is about one half of the total length of the guard 
cell apparatus. (See Table V.) The width of the pore is usually 
less than one half its length. The largest stomata were found on the 
upper epidermis of Triticum sativum, with a pore 39 microns in length; 
the smallest stomata were found on the upper side of Impatiens sultani 
with a pore six microns in length. The stomata which were measured 
