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STOMATA AND HYDATHODES IN CAMPANULA 
RO TUNDIFOLIA L„ AND THEIR RELATION TO 
ENVIRONMENT 
By MARGARET W. REA, B.Sc. 
Queen’s University, Belfast. 
(With 6 figures in the text.) 
M any authors have commented on the varying number of sto¬ 
mata observed either on the leaves of related plants, or on 
the leaves of plants belonging to widely differing families. Very 
little work so far has been done, by using the same species grown 
under different conditions, to demonstrate the possibility that the 
number of stomata per unit area may vary according to the leaf 
surface and the position of the leaf on the shoot. In this connection 
Professor R. H. Yapp found in Spiraea Ulmaria L. ( = Ulmaria 
palustris Moench.) a range from about 300 to nearly 1300 stomata 
per sq. mm. on the under surface (there were practically no stomata 
on the upper surface) for the lower and upper leaves respectively 
of the same shoot( 7 ,p. 827 ). He states: “It may be that Spiraea 
Ulmaria is exceptional in the latter respect, but it would be worth 
while comparing the successive leaves of a number of other plants, 
for if the phenomenon is at all general, the numbers already pub¬ 
lished for a large number of species might need considerable re¬ 
vision.” 
HISTORY. 
Weiss(6, pp. 166 - 167 ) was one of the earliest workers who com¬ 
pared the numbers of stomata occurring in a large series of different 
plants. He found that members of the same family or even members 
of the same genus may show great differences in the number of 
stomata present, although the habitat, temperature and amount 
of moisture in the soil is the same (6, pp. 166 - 167 ). His conclusion is 
that habitat has no influence on the occurrence of the stomata. 
The halophytes, such as A renaria grandiflora (6, pp. 123 - 132 ) and Cheno- 
podium ambrosioides , had more stomata on the upper than the 
