Margaret W. Rea 
58 
Hydathodes are not considered in relation to the stomata in 
any of the above papers. It was hoped that a comparison of the 
leaves of shoots of Campanula rotundifolia grown under different 
conditions would add something to our present knowledge of the 
distribution and other characters of the stomata and hydathodes. 
STOMATA. 
This investigation was begun to see whether the number or 
other characters of the stomata, such as their arrangement and 
size, vary on the lower and upper surfaces of the same leaf, or on 
the different leaves of the same plant, or on the leaves of different 
plants grown under varying conditions. 
Results. 
In the method finally adopted for determining the total area 
of the leaf, each leaf was placed directly on squared mm. paper, its 
outline was drawn and the number of squares within the outline 
was counted. After being cleared in eau de Javelle and stained 
slightly with Bismarck brown, the total number of stomata for 
each surface was counted and from the data obtained the average 
number of stomata per sq. mm. was estimated 1 . 
Basal, intermediate and upper linear leaves were examined 2 
(see fig. 1), and it was found that the number of stomata per sq. mm. 
for the under surfaces of each leaf was almost equal, the upper 
surfaces on the other hand showed a rapid rise from the lower to 
the upper leaf. 
Under 
Upper 
surface 
surface 
Upper leaf 
... 120 
67 
Middle leaf 
... 120 
54 
Lower leaf 
112 
14 
“ Whole” shoot 3 . From the lowest leaf upwards the under sur¬ 
faces showed a fluctuating rise. The upper surfaces of the leaves 
showed a marked rise, especially near the apex of the shoot. The 
average for both was highest for the upper leaves (see Table I, 
p. 62). 
1 The midrib was included in the estimation of the area of the leaf. The 
inclusion of the midrib, on which some stomata were always present, makes 
the number of stomata per sq. mm. slightly less than would otherwise be the 
case. The smaller veins did not affect the distribution of the stomata. 
2 From a shoot gathered on Benevenagh Mountain, Co. Derry. 
3 Grown in a garden, under normal conditions. 
