6 4 
Margaret W. Rea 
Conclusions. 
The average number of stomata per sq. mm. on the upper 
surfaces shows a steady rise from normal to sunny conditions (see 
Tables II to IV, pp. 62 and 63). This is not the case for the under 
surfaces, a probable reason being that the lower surfaces of leaves are 
always more or less in shade independent of habitat. The stomatal 
curves (see figs. 3-5) for the normal and shade shoots overlap: this is 
possibly due to the fact that the lower leaves of the normal shoot 
were shaded by other shoots. 
The difference in the total number of stomata for the under and 
upper surfaces respectively of the “whole,” normal, shade and sun 
shoots is instructive (see Tables I, II, III and IV, pp. 62 and 63). 
The normal shoot has about three times as many stomata on the 
under surfaces as on the upper; the shade shoot has more than three 
times the number on the under surface as compared with the upper, 
while for the sun plant the numbers approximate much more nearly 
for both surfaces. The “whole” shoot was grown under normal 
conditions, but the early summer of 1917 was drier and warmer 
than that of 1920 and this would account for the higher average 
number of stomata per sq. mm. compared with the number for 
the normal shoot examined in 1920 (see Tables I and II, p. 62). 
The average number of stomata per sq. mm. for the under and 
upper surfaces of all the leaves of 
the shoots 
taken together was as 
follows: 
Under 
Upper 
surface 
surface 
Sun shoot 
97 ‘ 21 
73*4 
“Whole” shoot 
in -93 
50*63 
Normal ,, 
89*5 
32-12 
Shade „ 
100-96 
29*5 
It is evident that numerically the sun plant has more stomata 
per unit area than the other shoots, especially on the upper surface; 
and suggestions are put forward later to account for this fact. 
Professor Yapp’s work showed that the stomata increased in 
number on the higher leaves of Spiraea Ulmaria and did so more 
markedly on the plant growing in a sunny situation. Although the 
stomata occurred only on the under sides of the leaves, those data 
have more bearing on Campanula rotundifolia than any of the other 
work cited. Contrary to Tschirch’s results, Campanula rotundifolia 
has more stomata per unit area in the sunny exposed situation than 
in the normal or shade conditions. This latter point is clearly shown 
