lO 



III. EVOLUTION OF GENERA AND SPECIES 



Every orchid is descended from a long series of ancestors. The slender thread of 

 life has come down to us unbroken through thousands, perhaps millions of years. 

 Most genera are the embodiment of a special idea or constructional plan. Tribes like 

 NeottL, Ophrydea., etc., are not composed of genera based on a common archi- 

 tectural scheme, but of genera often widely differing in conception and construction 

 which have a few characters of a general nature in common. Evolution is from the 

 simple to the complex. It is not always continuous, but appears to stop when he 

 end in view has been attained. In this work an ancient genus means one which has 

 probably existed from remote ages in more or less its present form. 



As no help is obtainable from fossil remains the comparative age of a genus can 

 only be inferred from the following considerations: 



(i) The simplicity or complexity of its organisation, and the degree of speciahsation 



^""(2) Thi extent to which it has become differentiated from the type of its tribe. 



(^) The number of species into wliich it has had time to expand. 



U) The extent of territory occupied. The wider its distribution the greater the 

 time required for such extensive colonisation. Genera havmg their headquarters m 

 America and two or tliree outposts in Europe, such as Coral/orh^z^, f''^"'^^^ ^^c-' 

 or headquarters in Europe with a species or two m America, such as Ep^pactts, 

 indicate an antiquity gomg back to the remote geological era when there was no 

 impassable barrier against the migration of plants between the Eastern and Western 



^''ThTorchidace^ belong to the Monocotyledons in which the basal type of flower 

 has sk stamens and thre^e stigmas, but of which some families have the stamens 



reduced to three. , , j j r 



The following considerations suggest that the Orchidacea^ may be descended from 

 the Apostasiace^a., a famUy of Indo-Malayan plants considered to be orchids by 

 R Brown, Bentham, etc. The latter assigned them to the Diandr^, doubtless because 

 ■n. Apostasta, the first genus to be discovered, the anthers a^ and a^ are fertile as 

 in th; Diandr., and in some species the anther A^ is reduced to a stammode. They 

 both have the minute seeds of the Microsperm^. Lmdley, however, and H. N. Ridley 

 (who had the great advantage of seemg nearly all the species in their native habitats) 

 consider the Apostasiaceae a distinct family. I 



The subsequent discovery of the Apostasian genus Nemriediav^^th three fertile anthers 

 altered the position, as it could not logically be included m the Diandra.. Phtzer there- 

 I J 3. p. 55 5 (i886), and Flora of the Malay Peninsula (1924)- 



