March, 1922] NEWCOMBE — BEHAVIOR OF SENSITIVE STIGMAS IO9 
a. Effect of the Germination oj Pollen on the Stigma 
It cannot be the germination of pollen followed by the penetration of 
pollen tubes into the tissue of the stigma that causes the stigma to remain 
closed after the primary closing. For I have found none of the pollens, 
under the most favorable conditions, on the stigmas or in sugar solutions, 
germinating in less than two hours. Indeed, in only three tests have I 
found it germinating in less than six hours. The stigmas, however, of all 
species so far reported by others, as well as those under my own observa- 
tion, open in most cases, in temperatures of 18° or above, within 30 minutes 
of the primary closing, provided no pollen has been placed on the stigmas. 
In such time relations, it may be assumed that the pollen has some effect 
in keeping the stigmas closed; but it cannot be the germination of pollen. 
Nor can it be the germination of pollen which causes the secondary closing 
of the stigmas; for, in the first place, many examinations of mine have 
shown that the pollen does not germinate on stigmas in ordinary weather 
till the stigmas have closed; and, in the second place, when pollen does 
germinate on stigmas in very moist air, the stigmas do not close. 
b. Withdrawal of Water from the Stigmatic Cells 
Burck (12) found that if he pollinated the stigma of Tofenia fournieri 
with dry pollen and closed the stigma, the stigma remained closed; but if 
he used moist pollen the stigma soon opened again. From this behavior, 
he inferred that it was the withdrawal of water from the stigma that kept 
the stigma closed. 
Lloyd (14), by observing the local curvature of the stigma lobes of 
Diplacus glutinosus when pollen masses were placed on different spots on 
the inner surfaces, came to the same conclusion as Burck. 
Brown (15), using Martynia proboscidea, could load the stigma lobes 
with sand or could give them a little quartz flour without causing closing. 
When, however, he used a large quantity of quartz flour, the stigma closed. 
From this behavior, he inferred, with Burck and Lloyd, that it is the with- 
drawal of water from the cells on the inner side of the lobes that causes the 
secondary closing. 
My own rather extensive work on the cause and conditions of secondary 
closing may be narrated under three sub-headings. 
I. Relation of closing to atmospheric moisture. Among the several 
species reported in this paper, two distinguish themselves from the others 
in that the bilabiate corolla has a closed throat, and the plants themselves 
grow in water or only where the substratum is very wet. These species are 
Utricularia vulgaris and Mimulus glabratus var. Jamesii. Seven individual 
flowers of the former and eight of the latter were cross-pollinated and the 
stigmas closed, but all stigmas opened soon afterward and did not subse- 
quently close. Nevertheless the ovules of Utricularia were fertilized; but 
