518 THE FERTILISATION OF FLOWERS. [PART III. 
376. ARIsTOLOCHIA SrpHo, L. (178, 349, 360).-—In this species 
the corolla maintains the same position during the whole period of 
flowering. Its lower part is directed straight downwards, and then 
with a sudden bend turns directly upwards; it is moderately wide, 
and the mouth is provided with a three-lobed lip. In this species, 
as in the previous one, we find flies imprisoned during the first 
stage, while the stigmas alone are ripe; they fertilise the stigmas 
with pollen brought from other flowers, and remain caged until 
the stigmas wither and the anthers shed their pollen. 
The reason why they stay imprisoned so long seems to me still 
insufficiently explained. In Delpino’s opinion, to which Hilde- 
brand assents, the smooth sides of the tube prevent the flies 
creeping up, until the withering of the flowers affords them foot- 
hold. This explanation. can only be correct if that part of the 
tube which slopes downwards from the entrance is distinctly 
smoother than the other portion which leads up from the lowest 
part of the tube to the expanded terminal chamber; for if both 
are equally smooth the flies will have as much difficulty in 
climbing up into the stigmatic chamber as in climbing back out 
of the flower. In Arum I have repeatedly noticed that the small 
midges try to escape from their prison, not by creeping, but by 
flying towards the light, and get knocked down by the grating at 
the mouth of the flower. So if in Aristolochia Sipho the inside 
of the tube is all so smooth that flies can climb neither one way 
or the other from the lowest part, the reason of their imprisonment 
must be sought only in the curvature of the two ends of the tube, 
the one rising straight from the lowest part to the cage, while the 
other part which rises up towards the entrance of the flower is so 
bent outwards at its upper end that the insects flying towards the 
light knock against the bend and fall back again. They are set 
free by the shrivelling up of the corolla, which enables them to 
creep out. 
Delpino found in the cage: (a) Muscidw : (1) Lonchea tarsata, Fallen ; 
(b) Phoride: (2) Phora pumila, Mgn. I found: Muscide: (1) Sapromyza 
apicalis, Loew, very ab. ; (2) Myodina fibrans, L., scarce ; also a small black | 
gnat, very ab., which I was unable to identify. 
Aristolochia altissima, Dsf., A. rotunda, L., and A. pallida, W., 
show only slight variations from A. Clematitis, according to Delpino 
(178). 
A. Bonplandi, Ten., unites the form of corolla of A. Sipho with 
the transitory hairs of 4, Clematitis (360). 
