236 LHe GRCHID.: REVIEW, [AUGUST, 1923- 
NOTES ON THE SEGMENTS OF ORCHID FLOWERS. 
(Continued jrom page 177.) 
N our last chapter on the segments of Orchid flowers, consideration 
was given to the structure of the labellum, and some of the forms it 
assumes. We may now continue our remarks on this organ, for it possesses: 
many features that are of importance in distinguishing the various genera. 
The nay Saccolabium derives its name from saccus, a bag, and labium, a 
lip, in efetence to the saccate 
labellum. An illustration is 
here given of Saccolabium: 
bellinum, the most generally 
cultivated species of the genus. 
The majority of Saccolabiums:- 
are natives of British India, 
and a few are scattered over 
the Malay Archipelago. 
In Cypripediums this sack-like formation of the labellum is seen in a. 
much more developed state, for it takes the form of a slipper-like pouch. A 
glance into the interior of this pouch will show that its formation compels 
insects searching for honey-like food to pass out of the flower by one of two 
passages, and in so doing remove the pollen and carry it to the next flower 
visited. 
In Pterostylis, a South Australian genus whose representatives are 
commonly known as “ greenhoods,” the labellum is irritable, so that when 
touched it flies up against the column. This interesting method of ensuring 
fertilisation has been well described by Dr. R. S. Rogers, who in his: 
“South Australian Orchids,” includes an illustration of Pterostylis curta, 
and remarks that ‘‘ If you examine the tongue you will find near the point, 
where its hinge is attached to the column, a peculiar little semi-circular 
apparatus something like a watch spring, with a small tuft of hairs at its 
freeend. This is called the appendage. The slightest weight on this tuft 
when the flower is erect will make the appendage act like a lever and cause 
the tongue to fly up against the hatchet-shaped wings of the column, where 
it will remain for a considerable time. It then gets ‘tired’ and falls down 
again. Besides the lever action, however, the appendage is also ‘ sensitive ” 
when it is not ‘tired.’ The flower has thus as it were two strings to its 
bow, by either of which it may bring about fertilisation. If even a very 
small insect visits it when ‘tired,’ it will imprison the insect as soon as it 
touches the appendage, and fertilisation will then take place exactly as in 
the caso of P. vittata. On the other hand, should an insect visit it when 
‘tired,’ there is still a chance that the weight of the visitor may be sufficient 
SACCATE LABELLUM OF SACCOLABIUM BELLINUM. 
