Ii8 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
After the primary closing at the time of polHnation, the stigmas that 
open close again 2 to lo hours after the opening, unless the air is very moist. 
The significance of this secondary closing is well indicated by the fact that 
pollen will not germinate on the open stigma unless the air is well nigh 
saturated. Utricularia vulgaris and Mimuliis glahratus var. Jamesii, having 
closed flowers, do not keep their stigmas closed after closing at the time of 
pollination, but the pollen germinates on the open stigma lobes. Except 
for the two species just mentioned, the germination of the pollen on the 
stigmas is secured either by continuous closure of the stigmas from the 
time of pollination, or by a secondary closing in those cases in which the 
stigmas open after pollination. 
As is well known, the sensitive stigmas under consideration reopen as 
often as closed, provided no pollen has been placed on the stigmatic surface. 
When pollen is placed on the stigma and the lobes are closed, the stigma 
may open within an hour, as it regularly does in Diplacus, or it may never 
open again, as is usual in Tecoma and frequent in several other species. 
Also the pollen may be artificially placed on the stigma so gently as not to 
cause closing. In this last case, the stigma remains open for two to ten 
hours, and then closes unless the air is very moist. In any event, the stigma 
is usually closed lo hours after pollination. By what agency is the primary 
closing maintained, and the secondary closing caused? It has been sug- 
gested by previous writers that the withdrawal of water by the pollen is 
the cause of the closing, and that the phenomenon is purely physical. 
Numbers of experiments have been reported in this paper which seem to me 
to indicate that the continued closure of the stigmas is more than the simple 
abstraction of water. Inorganic powder, like emery flour, is not effective 
at all in keeping the stigmas closed, though by capillarity it should withdraw 
water from the closed stigma. Pollen killed in hot water and dried does 
not keep the stigmas closed, though it retards somewhat their opening. 
Wet pollen and dry pollen keep the stigmas closed equally well. Flour and 
starch keep the stigmas of Tecoma closed about as well as does living pollen, 
but the stigmas of Torenia and Catalpa open finally when given flour or 
starch. The enzyme known as Taka-diastase, either in pure powder or 
mixed with starch, causes the stigmas of Torenia and Catalpa to remain 
closed for 3 to 10 hours, but nearly all the stigmas finally open. The Taka- 
diastase, with its enzyme destroyed by hot water, then evaporated, pow- 
dered, mixed with starch, and placed on stigmas, keeps the stigmas closed a 
shorter time than does the mixture of the normal Taka-diastase and starch. 
Casein alone does not affect the closure of the stigmas of Torenia, nor does 
a mixture of peptone and starch. This statement of results with different 
species shows how impossible it is to generalize by the study of a single 
species, and it might be that the behavior of several similarly acting species 
would not lead to a correct interpretation applicable to all. 
The one statement which seems possible to make is that, with the ex- 
