354 Transactions.— Botany. 
points of the lateral sepals (see /., Fig. B.), yet the slightest touch is sufficient 
to cause it to move quickly up to the column, when it occupies the position 
shown in Fig. C. On this movement of the lip the fertilization of the plant 
depends. 
If we take a flower, and gently touch the lip, so as to cause it to perform 
the motion just described, and then examine the position of the parts, we see 
that each side of the flower is narrowed inwards in a curved line parallel to 
the position now occupied by the margins of the lip, so that the posterior part 
of the flower forms a chamber, to which the lip, resting against the wing-like 
appendages of the column, is a tolerably close fitting door. 
Now let us suppose that an insect were to enter a freshly opened flower. 
The only entrance is between the tips of the lateral sepals, and here the apex 
of the lip is placed exactly where our visitor would probably alight. At first 
the weight of the insect would most likely counteract the natural tendency of 
the lip to move inwards, but as the insect crawls further into the flower, this 
would have less effect, until at length the irritability of the lip would enable 
it to overcome the resistance offered, and to spring back to the column. If 
no capture is made the lip soon regains its former position, but if the insect is 
imprisoned it remains firmly appressed to the column while its prey continues 
to move about. For the prisoner there is now only one mode of escape. This 
is by crawling up the column, passing over the stigma and viscid rostellum, 
and finally emerging from between the appendages of the column, directly in 
front of the anther. This passage, however, is so narrow and confined that-it 
would not be possible for an insect to pass through without brushing against 
the rostellum, and detaching portions of its viscid surface. If the insect were 
now to touch the anther, and it is difficult to see how it can escape without 
doing so, one or more of the pollen-masses, lying loose in their cells, would 
become glued to the viscid matter on the insect’s back, and consequently be 
withdrawn from the flower. To understand the mode of fertilization we have 
now only to suppose that the insect, with the pollinia attached to it, visits 
another flower, and is again imprisoned, when it is evident that in its efforts 
to escape it would pass over and in front of the stigma, which is sufficiently 
adhesive, when touched, to draw off a portion of a pollen-mass, or even a whole 
one, from the back of the insect. 
After careful and repeated examinations of living plants, I adopted this 
view of the fertilization of P. trullifolia as the only one explaining the various 
facts I had collected ; bnt, in order to satisfy myself that the lip really plays 
the important part I had supposed, I selected twelve flowers which were just 
expanding, and removed that organ from the whole of them. After a week or 
two, when they had closed and commenced to wither, I gathered them and 
examined their stigmas and pollinia. Not one flower was fertilized, and not 
a single pollen-mass had been removed. 
