94 PLANTS AND ANIMALS 
any of our native Orchids grow. In these, the most 
highly specialized of all plant groups as regards pol- 
lination by insects, the general arrangement of the 
flower is often somewhat similar in a general sense 
to the last case; but here the sepals and petals which 
between them form the platform, tube, sides, and roof 
of the flower, are all separate and often differently 
and elaborately coloured. The essential organs are 
greatly modified and hardly recognizable at first. 
There is only one stamen, producing two clusters of 
pollen, which are embedded in the roof of the flower. 
Each possesses a slender stalk which terminates in a 
little sticky disc which projects from the general sur- 
face. The pollen grains are held together in a mass 
by fine threads, and the whole with its stalk—the pol- 
liniwm—resembles a lemonade bottle in shape. The 
stigma is also embedded, forming a sticky surface in 
the roof of the flower behind the stamen. When an 
insect inserts its head into the flower, its forehead 
comes in contact with the sticky ends of the pollinia, 
which adhere, so that on leaving the flower the insect 
flies away with the pollen sticking to its forehead like 
two little horns. And now a remarkable thing hap- 
pens. The stalks of the pollinia, drying rapidly in the 
air, contract unequally, and become curved, so that 
the pollinia bend forward into a horizontal position. 
When the insect visits another flower and thrusts in 
its head, the pollen consequently comes in contact 
with the sticky stigmatic surface farther down the 
tube, and cross-pollination is effected. 
In the cases of many of these highly specialized 
flowers, one is no less struck with the perfection of 
the arrangements made for preventing self-pollina- 
