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AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
same species as Heckel, found the stigma lobes sensitive on the inner faces 
only. Burck (12) found both surfaces sensitive, but the inner surface the 
more so. Lloyd (14), by probing the stigma of Diplacus glutinosus with a 
dull-pointed glass rod, was convinced that the lobes are sensitive on their 
inner faces only, and that a response is brought about only when the cells 
of the inner faces are stretched by the bending of the lobes. 
My own work in determining the location of the sensitive area of the 
stigma has been done on Catalpa bignonioides, Tecoma radicans, Torenia 
fournieri, and Utricularia vulgaris. In Catalpa, the lobes are sensitive on 
both the inner and outer surfaces, though more sensitive on the inner. In 
the other three species, the lobes are sensitive on their inner surfaces only. 
To determine this result, the following method was used, except for Utric- 
ularia, which has but one sensitive lobe, the other being small and not 
motile. The flower was secured with its pedicel between the halves of a 
cork held by a clamp. The corolla and stamens were then removed. Next, 
one lobe of the stigma was seized by a fine forceps and bent back out of the 
way of the other lobe, the object being to prevent the two lobes coming 
into contact during the manipulation. With any kind of a blunt probe, 
one may now explore the free lobe for the sensitive region. By this method, 
the lobes of Tecoma, Torenia, and Utricularia may be pushed about at will — • 
from 20 to 50 flowers were used for each species — as long as the probe is 
against the outer surface only; or percussion may be used on the outer 
surface without bringing a response. The same sort of treatment will, 
however, cause the prompt closing of the stigmatic lobes of Catalpa. The 
sensitiveness of Catalpa to pressure on the outer faces of the stigmatic 
lobes shows that the condition for reaction that Lloyd found for Diplacus 
glutinosus — the stretching of the cells of the inner face of the stigma — does 
not obtain for all species; for one can hardly believe that pressure on the 
back of the lobe will cause the elongation of cells on the inner face. The 
question must be left open, however, as to whether the stimulus on both 
the outer and the inner faces of the stigma of Catalpa is due to pressure or to 
stretching of cells on the respective faces. 
That the body giving the stimulus need not be solid has been shown by 
obtaining the same responses when using a fine jet of air against the stigma 
lobes of Tecoma radicans, Torenia fournieri, and Utricularia vulgaris. 
Besides the pressure stimulus, there is no doubt that an electric current 
through the stigmas may induce the primary closing. Kabsch (2) notes 
this for Mimulus guttatus, and I have had the same result with Catalpa 
bignonioides. Heckel (8) records the vapors of hydrocyanic acid, acetic 
acid, ammonia, chloroform, ether, etc., as inducing primary closing, and 
Correns (11) found the same for ammonia vapor and reduced oxygen 
pressure. Lloyd (14), however, showed that heat, alcohol vapor, and 
liquid alcohol cause the closing of the stigma of Diplacus glutinosus only as 
they kill the stigma. I have found the same relations in the behavior of 
