DEVELOPMENT OF PLANTS 



389 



flowers of the canna and determine the significance of the position 

 and movement of the labellum and its relation to the stamen and 

 stigma. 



135. Orchidales, the Orchid Order. The orchids are the 

 highest group of the monocotyledons and their flowers are a 

 source of wonder and admiration, owing to the singular beauty 

 and delicacy of their mechanical construction. Variation in this 

 order has occurred on a gigantic scale, resulting in a larger num- 

 ber of species (over 7,000) than is found in any of the preceding 

 orders. Nevertheless these elaborate variations have not been 

 very successful in enabling them to compete with other plants, 

 and as a result the orchids are rather rare and not at all com- 

 parable in number of individuals with the lilies and grasses. 

 Though more widely distributed than any of the other monocoty- 



FIG. 291. An epiphytic orchid growing upon the branch of a tree. The 

 coarse roots, r, are surrounded by a mantle of cells which take up the mois- 

 ture from the atmosphere, b, storage organs formed from the base of the 

 leaves, enabling the plant to produce flowers and fruit. The smaller stalks, 

 a, are the shrivelled remains of these organs after flowering and fruiting. 



