ORCHIDS. OF 
The column is elongated, and has near its upper extremity 
two quadrangular wings, produced forwards at right angles. 
The anther is terminal, 2-celled, and contains four granular 
pollinia. The stigma is a 2-lobed elongated surface on the 
face of the column, just below the projection 
of the wings. When an insect enters the 
flower and crawls to the bottom, the label- 
lum moves forward and shuts it in, so that it 
can only escape by walking up the column 
and out between the wings. But in doing 
so it has first to pass the stigma, and then 
the rostellum, in touching which it will carry is 
away with it one or more of the pollinia. ol 
If it visits a second flower the same process Fig. 192. Column 
will be repeated, but this time the stigma % e terostylis, 
will be smeared with the pollen brought from qm, anther: », ros 
the first-visited flower.* tellum; st, stigma. 
(o.) The structure of orchid-flowers is apparently so different 
from that of the two types previously examined that it is not 
easy at first sight to see any relationship between them. In 
both iridaceous and liliaceous plants trimerous symmetry 
prevails in all the parts, there being 6 perianth-leaves, 3 or 6 
stamens, and usually a 3-celled ovary. In orchids we also 
find the 6-leaved perianth and 3 placente in the ovary; but 
the staminal whorl appears to be defective. At the same 
time one of the perianth-leaves—yiz., the labellum—is always 
different in appearance from 
the others, while, further, 
there are in most orchids “a _ 
peculiar outgrowths, both . Ad 
of the labellum and column, | Ce) 
which are not explicable 
by superficial examination. nie oat a 
But by careful dissection it . a2 
has been shown pretty con- 
clusively that the flower 
consists theoretically of 5 A2 OAs 
whorls of 3 parts each—viz., a 
3 sepals, 3 petals, 6 stamens, 
and 8 carpels. By tracing 
out the 15 groups of spiral 
vessels which pass up into Fig. 193. Theoretical floral diagram of 
the flower, Darwin (whose an Orchid flower (after Darwin). 
* The structure and development of. this group of flowering plants is 
fully treated of in Darwin’s “ Fertilisation of Orchids.” Papers on the 
fertilisation of New Zealand species, by Mr. T. Cheeseman and the present 
writer, will be found in the “‘ Transactions of the N.Z. Institute,” Vol. v., 
p. 352; vii., p. 849; ix., p. 542; x., p. 353; xi., p. 418; and xiii., p. 291. 
7 
