ORCHIDACE^. 381 



All these structures are very cleverly and wonderfully 

 adapted for causing the transference of pollen from one flower to 

 another by insects which are attracted as a rule by honey 

 secreted in the sac or spur of the lip. The mechanism varies 

 very considerably and orchids are so highly specialised in this 

 respect that often pollination fails and no seeds are set simply 

 because the proper insect for that species has not visited the 

 plant. In general the head or proboscis of a bee, probing the 

 spur for honey, touches the rostellum which adheres to it, so 

 that when the insect flies away the anthers open, and the polli- 

 niums are dragged out and carried off. A bending of the stalk 

 of the pollinium as it dries during the insect's flight may, if 

 necessary, bring the pollen-mass into such a position that in 

 another flower it touches the stigma. The elasticity of the 

 connecting band or of the thread which binds the groups of 

 pollen together allows of some being left on the stigma while the 

 rest may be carried to another flower. 



The fruit is a capsule containing an enormous number 

 of very small seeds which are easily carried by the wind, 

 and this perhaps explains why so many orchids grow 

 high above the ground on the branches of trees. 



The vegetative parts vary also considerably. There is 

 always a perennial root-stock ; but this may consist of tubers 

 or of a creeping rhizome. In some the shoot grows on year 

 after year bearing flowers laterally (a monopodium, t. 249), in 

 others it finishes each season's growth with an inflorescence 

 (sympodium, t. 243). 



Throughout the family there is a remarkable diversity in the form of 

 the flower which may even imitate the appearance of some insect (e.g., 

 the Bee and Fly orchids ot England). The size, brilliancy and lasting 

 qualities of many species have made them favourites with horticulturists 

 who are constantly producing hybrids. 



The family is one of the largest among flowering plants, 

 having over 400 genera and 5,000 species. Of these 1,600 

 have been found in India, most of them peculiar to the country. 

 The south-east Himalayas, Assam and North Burma is the 

 richest area : the Deccan is comparatively very poor. 



J Pollen sacs together on the top of the column . . . b 



\ Pollen sacs on either side of column. Ground orchids . h 



, ("Ground orchids . . . . . c 



I Tree orchids ......... . . f 



