DEVELOPMENT OF PLANTS 



423 



organ is the most striking feature of the orchid and it assumes 

 an almost endless variety of forms and colorations, being a good 

 illustration of Wallace's law that the most highly modified part 

 shows the greatest variation in coloration. In Cypripedium (Fig. 

 292, A) the labellum assumes the form of a moccasin, in other 

 genera it resembles a vase, boat, tongue, body of insect, etc. It 



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

 coarse roots, r, are surrounded by a mantle of cells which takes 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 shriveled remains of these organs after flowering and fruiting. 



is entire or variously lobed, slit, fringed and often prolonged into 

 a tube for the concealment of nectar. The stamens and stigmas 

 are reduced in number and greatly modified, the former organs 

 usually being reduced to one and so fused with the style that the 

 anther is sessile upon it (Fig. 292, B). One or two of the stig- 

 mas are generally modified into a mucilage-secreting organ, called 

 the rostellum (Fig. 293, A). The microspores are usually united 



