SECT. xm. THEORETICAL STRUCTURE. 403 



Mr. Eobert Brown was the first to observe, that an 

 orchid flower consists of fifteen organs, arranged alter- 

 nately, three within three, in five whorls. This accords 

 perfectly with a -system of spiral vessels developed at an 

 early age in all orchids. Mr. Brown and three of the 

 greatest living botanists 5 have each traced the spirals 

 from six bundles surrounding the ovary in the footstalk 

 to the different organs of the flower, and have found 

 that they consist of fifteen bundles corresponding to the 

 fifteen organs of the flower ; namely, three sepals, three 

 petals, six anthers in two whorls (three of which are 

 rudimentary), and three pistils, with their stigmas : 

 these are arranged in alternate whorls, and undergo 

 many modifications. The pistils and anthers are con- 

 fluent, and form the column ; the uppermost stigma 

 becomes the rostellum; the three inner anthers are 

 rudimentary, one forming the front of the column, and 

 the other two forming the membranous sides of the 

 hood which protects the pollen ; and, lastly, the two lower 

 anthers are united to the sides of the lowest petal, and 

 form the labellura, which accounts for its great size, 

 frequent tripartite form, and peculiar manner of attach- 

 ment. 



This system has been wonderfully modified to pro- 

 duce the varied groups of extra-tropical and brilliant 

 forms of exotic orchids, yet it can be traced in all. 



* Messrs. Hooker, Darwin, and Brongniart. 



