432 
POPULAR SCIENCE REVIEW. 
free^ and attaching itself to whatever has caused the fissure of 
the membrane_, is withdrawn with its adherent pollen-masses. 
The stigma lies beneath the rostellum^ with a projecting sloping 
surface ; its lower edge fringed with hahs. 
The tubular flowers of this species are arranged in a spike^ 
each flower standing out horizontally. The labellum is fur- 
nished at the base with two globular processes^ in which an 
abundance of nectar is secreted^ which falls into a receptacle 
beneath. The entrance to the nectary beneath the lower 
margin of the stigma is very contracted. When the flower 
first opens^ there is nectar in the receptacle_, but the rostellum 
and labellum approximate so closely^ and so narrow a channel 
is left_, that only a fine bristle could be passed down into the 
nectary. In a day or two^ the labellum retreats further from the 
rostellum_, and a wider channel is opened. This circumstance 
is important to the fertilization of the species. 
Most Orchids have their flowers open for some time before 
being visited by insects_, but^ in this instance,, the boat-shaped 
disc^ with its poUinia^ has been found to be removed soon after 
the expansion of the flower. At this period^ the passage to 
the nectary is so small^ that an insect could not thrust down, 
its proboscis^ without touching the furrow along the middle of 
the membrane covering the disc. This touch causes the 
membrane to spht^ and the boat-shaped disc is freed; its viscid 
fluid causes it to adhere longitudinally to the proboscis,, and,, 
as the insect flies away, it bears the pollinia with it. Here 
arises a difficulty : — Since the labellum lies so close to the 
rostellum, how could the pollinia possibly be conveyed to the 
stigma ? It has been observed, that, after a day or two, the 
channel is enlarged, and then there is no difficulty in the 
pollen-masses being placed in contiguity with the viscid 
stigma. From these circumstances, it must be concluded, that 
the pollen collected from an early-opened flower cannot be 
transferred to its own stigma, but to the stigma of another 
flower, which has been open for two or three days. We will 
again leave Mr. Darwin to explain in his own words : — 
Hence not only the pollen must be carried from one flower to another, as 
in most Orchids, but a lately expanded flower which has its pollinia in the 
best state for removal cannot then be fertilized. Generally, old flowers will 
be fertilized by the poUen of younger flowers, borne, as we shall see, on a 
separate plant. In conformity with this I observed that the stigmatic surfaces 
of the older flowers were far more viscid than those of the younger flowers. 
Nevertheless, a flower which in its early state had not been visited by insects 
.would not necessarily, in its later and more expanded condition, have its 
poUen wasted ; for insects, in inserting and withdrawing their probosces, bow 
them forwards, and would thus often strike the furrow of the rostellum. 
