March, 1922] NEWCOMBE — BEHAVIOR OF SENSITIVE STIGMAS III 
tree but little reached by the sun, and paper bags were tied over the panicles. 
The following day the bags were removed. The open flowers were then 
always found with open stigmas. Several panicles were brought into the 
laboratory and their stems were set in water. The open flowers were dis- 
carded, and a wait was made for the immature blossoms to open. When 
the blossoms were open and stigmas were open, the inflorescences were 
subjected to conditions which brought wilting, or to conditions preventing 
wilting. The result reached was that the stigmas close, without stimulation 
or the presence of pollen, as soon as the corollas show any wilting. The 
corollas show flagging very quickly in experimentation ; and quite generally 
in natural conditions on the tree — such temperature and moisture condi- 
tions as obtain the latter part of June and through July, when the trees 
are in bloom — the corollas are found flagging and the stigmas closed. My 
observations on the closing of the unpollinated stigmas because of wilting 
and the readiness with which incipient wilting takes place in the usual 
behavior of these flowers have extended to hundreds of flowers and have 
covered three flowering seasons. 
Assuming that the stigmas of Catalpa close without pollination, with 
incipient wilting of the flower, as shown in the preceding paragraph, one 
may next inquire whether the presence of pollen on the stigma will cause 
closing when there is no wilting. My notes show that 109 flowers have 
been used in trying to answer this question. It was found that if, after 
pollination without immediate closing of the stigma, precautions were 
taken to insure a very moist atmosphere, there was no subsequent closing. 
In an atmosphere not very moist yet moist enough to prevent wilting of 
the flower, the presence of pollen induced closing when in its absence there 
would have been no closing. 
With the flowers of Tecoma radicans, 17 stigmas were cross-pollinated 
without closing the stigmas immediately. The flowers were kept in the 
house, their pedicels dipping into water in beakers. The conditions were, 
therefore, fairly moist and there was no wilting. Only one of the 17 stigmas 
subsequently closed. Several unpollinated flowers lay on the table without 
water for 10 hours, and thus were allowed to wilt : but they showed no closing 
of the stigma. This series of tests is incomplete. It needs still the case 
of polHnation, without primary closing, in dry air, or with flowers on the 
vine, to see whether the secondary closing would ensue. That the presence 
of pollen on the stigma is effective in keeping the stigma closed after it has 
been stimulated mechanically to close was shown by Elrod (13); and 
numerous tests of my own confirm his results. 
2. Use of absorbent substances on the stigma. As stated before in this 
paper, Burck (12), Lloyd (14), and Brown (15) have expressed the view 
that the secondary closing of stigmas is due to the withdrawal of water 
from the inner surface of the stigma lobes by the pollen. There is no 
question that the presence of pollen in dry air either keeps the stigma closed 
