67 
Porometer in Stomatal Investigation. 
Ficus clastica , Phaseolus vulgaris , Helianthus annuus , Begonia (“ Gloire de 
Lorraine ”), Begonia (“ President Carnot ”), Aucuba japonic a, Richardia 
aethiopica , Saxifraga c or di folia, Moms nigra, Eupatorium Raffilli, 
Dracaena Godsejfiana , and Piper dilatatum. 
These are hypostomatous plants with the exception of Helianthus , 
Richardia , Saxifraga , and Dracaena , which are amphistomatous. The 
following experiment shows a typical result obtained with a hypostomatous 
leaf. 
Expt. 38. 26. xi. *14. 
A double chamber attached to leaf of Begonia (‘ President Carnot ’). 
The dimensions of the chamber were as follows : 
External diameter of inner chamber, i-o cm. 
External „ „ outer „ 3-5 „ 
so that the extra length of path traversed by the air when the outer chamber 
was closed was 1-25 cm. approx. Readings were taken during both the 
morning opening and evening closing of the stomata. The curve obtained 
is shown in Fig. 5. 
50 
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£ 40 
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5 30 
20 
o 10 
1 
1 
RECIPROCALS OF OPEN' READINCS [STOMATAL APERTURE] 
Fig. 5. Effect of the intercellular spaces of the leaf upon porometer readings. 
The points do not lie upon a smooth line, but this is not surprising 
since slight changes in the size of the intercellular spaces are probably 
of frequent occurrence. The chief point for consideration is that, with 
increasing size of the stomatal aperture, the relative part played by the 
