Stomata and Hydathodes in Campanula rotundifolia L. 71 
linear leaves is probably reduced to a minimum as the cuticle is 
slightly thicker than in the intermediate or basal leaves. It is 
generally recognised that of two leaves of the same volume, if one 
is flat and thin it will lose more by evaporation than a narrow 
thicker one. 
Thus towards the apex of the shoot the leaves show an approach 
to xeromorphy which includes the degree of development of the 
hydathodic organs. The number of hydathodes present bears a dis¬ 
tinct relation to the position of the leaf on the shoot. The above 
conclusions were applicable in varying degrees to the three leaves, 
to the “whole” shoot and to the normal, sun and shade shoots. 
The cotyledonary leaves appear to be exceptional, as although they 
were basal in position, a single apical hydathode group was present. 
3. The environment. 
From the fact that the hydathodes on the shade plant had more 
numerous and larger pores for comparable leaves than either the 
normal or sun shoots, it would seem that environment is an impor¬ 
tant factor in the development of these water-secreting organs. As 
they were most numerous at the base of the shoots, these pores are 
probably very efficient in getting rid of superfluous water. The 
danger of the internal tissues being flooded, in the absence of acces¬ 
sory means of increasing the water-loss, would be most acute in 
the shade and normal plants. The lower leaves were not present 
in the sun shoot, but the above suggestion would hold good, although 
the difference between that shoot and the normal one is not so 
marked. In such, a danger of internal flooding in the leaf would 
not be so acute, and further, the presence of a larger number of 
stomata on the upper surfaces of the leaves of the sun plant is 
probably correlated with this decrease in water-secreting pores. 
SUMMARY. 
Stomata. 
1. The number of stomata per sq. mm. varies in Campanula 
rotundifolia , increasing especially on the upper surface with a higher 
position of the leaf on the shoot; and on the under surface also 
with increase of illumination and dryness of the habitat of the plant. 
2. The increase in number of stomata per sq. mm. in the sun 
shoot as compared with the normal shoot is suggested to be due 
to increased photosynthesis, as involving the utilisation of more 
