192 Mr. W. Murton Holmes on the 
the extremely sticky tip of the rostellum, which sticks to the top 
of its head—a natural booby-trap. On leaving the flower the 
fly drags the two pollen-masses which are attached to the ros- 
tellum out of the anther, and goes away with them on its head. 
It now visits another flower, and again alights upon the foot- 
stool. Meanwhile the stalk of the two pollen-masses has bent 
forward, and as the fly puts its head in at the window the pollen- 
masses are left sticking to the wall of the stigmatic cavity. 
The transference of pollen to insects takes place in Cypripedium, 
the lady’s slipper, in a manner altogether peculiar. Part of the 
flower is shaped like a slipper, and its cavity is furnished at the 
bottom with hairs full of sap, and which also secrete nectar. 
Certain small bees are in the habit of entering to feast on the 
hairs. Three ways are open to them: the two small orifices on 
either side of the column, and the large opening in the middle of 
the slipper, and in front of the column. ‘They choose the last, 
and slip under the broad rough stigma to the bottom of the 
slipper. After a time they wish to escape into the open air 
again, but that is not so easy. The edges of the large central 
opening are bent inwards, and so fashioned that the bees cannot 
climb up them, and the bees have no choice but to make use of 
the two little exits at the back of the slipper. Even through 
these escape is not altogether easy, the bees being obliged to 
squeeze through the narrow opening. The result is that one 
shoulder brushes against the soft viscid pollen of the anther, 
which forms the inner border of the orifice. The last act in the 
story is the entrance of the insect with its shoulder covered with 
pollen into another Cypripedium flower, whose rough stigma is 
thereupon immediately besmeared with pollen. 
Crossing between neighbouring flowers occurs when these are 
crowded together. In the hemp agrimony there are five florets 
on each head, which open one after another. Younger and older 
flowers are therefore always close together. The styles are 
divided almost half-way down into two long thread-like branches 
bearing the stigmatic tissue only on their lower portion. The 
rest of the branch is thickly covered with bristly hairs. The 
styles are parallel and folded together as long as they are enclosed 
in the anther-tube, but afterwards elongate and push their way 
above the anthers, the hairs brushing the pollen from the 
anther-tube, and it adheres in abundance on the outer side of 
each branch of the style. The branches soon diverge at a con- 
siderable angle, and come in contact with adjacent styles, and 
when the pollen is detached from the hairs it falls upon the 
stigmatic tissue. 
The stamens of Veronica form a convenient resting-place for 
insects. Here the honey is hidden in the centre of the flower. 
To reach it the fly is obliged to hold on to the stamens, and so 
