EVOLUTION 13 



of England. Bngelhardtia, a tropical genus of the walnut family (Juglandace:e), now 

 confined to Malaya and Central America, occurred in Miocene times both in Europe 

 and N. America. Later, in Pliocene times, the climate became more temperate, and 

 many of the tropical plants of the earher Tertiary period disappeared, and in Gliostene 

 tmies even the sub-tropical forms of the Mediterranean region mostly died out. 

 Rawondia pjremica in the Pyrenees and Haberka rhodopensis in the Balkans, both of 

 which belong to the Gesneriacea;, now restricted to tropical or sub-tropical regions 

 persist m these localities to the present day, probably because, being adapted to 

 alpme conditions, they could better stand the change of climate.' 



The Diandrs and the Monandry form two great parallel lines of descent. The great 

 antiquity of the Diandras is shown by their world-wide distribution, tropical as well 

 as temperate, m Asia (their probable centre of distribution), Europe, and America 

 They have rhizomes and roots, but no tubers, no pollinia and no rosteUum, and have 

 single pollen-grains immersed in a sticky paste secreted by the anther. The fact that 

 they have only branched into four very closely related genera seems to show that 

 evolution has long ago reached its climax and stopped. Darwin says that Cypripedium 

 diiters from aU other orchids far more than any other two of these do from one 

 another". It forms "a record of a former and more simple state of the great Orcliidean 

 Order .2 * 



In the Monandry the most ancient and primitive genus appears to be Cephalanthera. 

 it IS the least diiferentiated from the monocotyledonous type of flower, for the anther 

 IS suspended from a filament, the pollen-grains do not cohere in tetrads, and there is 

 no rosteUum, in which points it diifers from aU other genera of the sub-order It 

 resembles Cypripedium by its rhizome and numerous roots, and by the employment 

 o± a narrow passage to compel insects to smear the thorax with very adhesive matter 

 and thus carry off the crescent-shaped poUinia affixed to their sticky backs. It came 

 as a surprise to find that the ancient types of ground orchids, such as Cypripedium, 

 Cephalanthera, Eppactis, Listera, Neottia, etc., are characterised by rhizomes and mono- 

 stehc fungus-mfected roots, and that we only meet with polystelic mostly fungus-free 

 tubers m the more recent and more higlily speciahsed Ophryde^. 



Cephalanthera _,s the most ancient and I tliink the only genus of terrestrial orchids 

 known to obtain the adhesive matter for affixing the pollinia to insects-not from 

 the anther, as in Cypripedium-hut by utilising the ordinary secretion of the stigma 

 whose normal function is the detacl^ent of pollen from pollmia brought into con- 

 tact with It by msects. In all other genera of the Monandry (with rare exceptions) 

 the upper stigma is transformed into a special organ, the rosteUum, which secretes 



LinnSn ^ety^ '^' ^^°^^ information I am indebted to Prof. F. E. Weiss, President of the 

 ^ Darwin, Pert. Orch. ed. 2, p. 226. 



