THE PLANT AND ITS HELPERS 79 



examination of the flower will show that the 

 petal forming the lip is carried backwards into a 

 spur which, although it contains no nectar, is 

 valued as a food substance in itself by bees. Now 

 the head of the insect in search of the succulent 

 tissue comes into contact with two sticky disks 

 attached to the stalks of the pollen masses ; so 

 that when the bee emerges the pollinia are carried 

 away. At first the pollen masses stand erect, but in 

 about half a minute, owing to a beautiful arrange- 

 ment whereby the base of the stalk contracts, 

 they incline forward. Thus by the time the bee 

 has arrived at the next flower the pollen masses 

 are in such a position that they cannot fail to 

 strike the stigma. The manner in which the 

 pollen masses are attached to the head of the bee 

 may be well seen if the point of a pencil is inserted 

 into the cavity of an orchid flower, and then gently 

 drawn away. 



It is not always that the plant, after attract- 

 ing the insect to pay a visit, is willing to let the 

 creature take its departure at once. In the case 

 of Aristolochia clematitis, gnats and other insects 

 are sometimes held prisoner for sixty hours until 

 the work which is required of them has been per- 

 formed. The essential organs are contained in a 

 kind of bulbous swelling at the base of the flower, 



