Stomata andHydathodes in Campanula rotundifolia L. 57 
under surfaces. This was also true of Conifers and Monocotyledons 
such as Asphodelus luteus and Iris germanica. 
Tschirch at a later date reviewed the work of the earlier writers 
and quotes Morren as considering that “ in related plants the number 
of stomata was in simple relation to the need for water.” Czech 
( 5 , p. 169 ) considered that plants, of the same organization and family 
with varying numbers of stomata, can close them at will and so 
guard against over transpiration. Zingeler ( 5 , p. 169 ), who worked with 
the Carices, found that those growing in a dry habitat had few 
stomata while those growing in a damp habitat had many. Tschirch 
( 5 , p. 173 ) concluded that on the whole plants in dry, stony places 
had fewer stomata than those growing in fields. In both habitats 
there were species with more stomata per sq. mm. on the upper 
than the under surfaces. 
Upper 
Under 
surface 
surface 
Triticum sativum ... 
47 
32] 
| 
Secale cere ale 
49 
4 2 
[ Fields 
A vena sativa 
40 
27J 
1 
Sedum album 
49 
251 
1 Dry, stony places 
Sedum acre ... 
21 
r 4 J 
r 
But Triticum and A vena have more or less isobilateral leaves 
while the species examined from dry, stony places were succulents. 
Miss Delf (2, p. 501 ) records that the number of stomata on Salicornia 
annua increased the higher the internode, and that their size varied 
with the age of the internode, being smaller on the upper leaves. 
From the fact that, although there were many stomata present in 
Salicornia annua, there were few in Suaeda maritima and Arenaria 
peploides , she concludes that “the distribution of stomata in halo¬ 
phytes is a variable feature and throws but little light on the 
problem of transpiration in these plants.” Yapp(7, pp. 826 - 828 ) found 
many more stomata per unit area on the upper leaves of Spiraea 
Ulmaria than on the lower leaves. He concluded that the larger 
numbers on the upper leaves were counterbalanced by the smaller 
size of the stomata, the hairiness and the thicker cuticle of the 
leaves; and also that, considering the stomata alone, the transpira¬ 
tion from the smaller but more numerous stomata of the upper 
leaves is not much greater than that of the lower leaves with the 
fewer but larger stomata. Darwin (l, pp. 436 - 437 ) considered that his 
experiments indicated that transpiration is regulated by stomatal 
aperture, because on the whole there was a parallelism in the curves 
of transpiration and of stomatal condition. 
