Sert.-Oct., 1918.] THE ORCHID REVIEW. 197 
the anther cells ; in the higher forms caudicles being developed by which 
they are attached to the viscid gland of the rostellum. The caudicles vary 
greatly as regards their development, and in the remarkable Bonatea 
speciosa they are over three times as long as the somewhat elongated 
pollen masses, yet both belong to the anther, while the viscid gland attached 
to the other end of the caudicle is formed by the rostellum, which is perfectly 
distinct from the anther in the early stages of the flower. 
The rostellum is a modification of the median stigma, and its primary 
function is to secrete a viscus to attach the pollinia to the bodies of the 
fertilising insects. In the higher forms it acquires additional and more 
complex functions, though always occupying a position subordinate to the 
pollinia. The primitive rostellum simply exudes a viscid fluid below the 
anther, which is first smeared on the body of an insect which visits the flower, 
and then becomes attached to the base of the pollinia as the insect retires, 
the result being that the pollinia are carried away, and left upon the stigma 
of the next flower visited. A later stage is that the outer surface becomes 
membranous, serving to protect the underlying viscus. Then the viscus 
acquires the property of drying very quickly on exposure to the air, and the 
membrane develops in different ways, regulating the shape of the gland ; 
in the Orchis group forming a complete pouch, which ruptures at a slight 
touch when an insect visits the flower. It may also dilate and assume the 
additional property of preventing the pollinia from falling on the stigma of 
the same flower. Again it may become trilobed, as in Habenaria and 
Bonatea, the side lobes forming elongated channels for the support of the 
caudicles of the pollinia. 
In the large tribe Vandez another remarkable development is seen, a 
part of the rostellum becoming separated as a zone of hyaline tissue, 
dehiscing at maturity and forming what is known as the stipes, to 
which the pollinia are attached at one end, while the gland is situated at the 
other end. When an insect visits the flower and touches the gland 
the whole combined organ comes away together. This stipes may be again 
subdivided longitudinally, forming two distinct stipes, each with a single 
Pollinium attached, and these may be attached to a single gland, as in 
tostachys, or to two distinct glands, as in Mystacidium. In some of the 
: y — Ophrydez the rostellum may also be divided, ene the appearance 
® rostella, though they are only divisions of one original one. 
Tn Catasetum there is a further development, for the two sexes are 
entirely Separated, yet in the male flower not only the stipes and gland of the 
Pollinia, but the sensitive antenne, which announce the visit of the insect, 
" free the mechanism which ejects the whole pollinary apparatus 
€ Insect’s back, with a sudden jerk, are developments of the rostellum, 
and thus are female in origin. The development is remarkable, quite apart 
