EVOLUTION jj 



with its dry habitats, the roots are shorter and thicker, suggesting the tubers of 

 Vlatanthera chlorantha, but monostehc with a single central cylinder (Text-fig. 9, p. 88). 

 All the above, with the continental Limdonm, form the tribe Neottie^ Lindl.' 



Spiranthes has its headquarters in N. America, with about 24 species, of which 

 one, S. Koman^offiana, has an outpost in Ireland, and perhaps in the Western Scottish 

 Isles, but IS found nowhere else in the Old World. Europe has only four species 

 of which S. ceshvalis extends to Asia Minor and Algeria, S. autmmtalis to Trans- 

 caucasia, Asia Mmor, Tunis and Algeria (Camus), whilst S. australis only occurs in 

 Europe m the Caucasus, extending to Asia, Australia, Tasmania and New Zealand 

 Tins very wide distribution of the genus points to an extremely ancient origin 

 especiaUy the extension of S. australis to Australia and New Zealand ' 



The tribe Malaxideas Lindl. is characterised by waxy pollinia. Many exotic epiphytes 

 belong to this tribe, of whose 350 genera only five are European. These five, except 

 Corallorhi^a, have a swelling of the stem (pseudo-bulb), the leaves embracing which 

 contam abundant elongated cells for storing water, a useflil provision for plants 

 growmg m wet ground wliich dries up in some seasons. It is a quite independent line 

 of descent, as compared with the Neottiea^. Malaxis paludosa has probably the simplest 

 form of rostellum m existence-a mass of cells which resolves itself into a viscid 

 drop. Corallorhi^a is a leafless saprophyte of low organisation with a coral-hke 

 rhizome and no roots. America seems to be the place of origin of Uparis, Malaxis 

 and Corallorht^a, whose antiquity is shown by the fact that one species of Corallorhi^a 

 has had time to colonise Europe, and one each of Uparis and Malaxis to spread 

 through Europe to Japan. There are large numbers of Uparis in New Guinea and 

 the adjacent islands. Epipogon is allied to Corallorhi^^a by its similar rliizome and 

 leafless flower-stem, and is probably descended from ancestors very near the latter 

 While, however, Corallorhi^a has stood still, Epipogon has attained a high degree of 

 evolution m the direction of Or.^/>, having beautiful flowers with a large^but inverted 

 spur pollmia on long caudicles, and a heart-shaped rostellum, which foreshadows 

 the division of the latter into two separate viscidia in the Ophrydes. It has perhaps 

 been evolved smce the isolation of America, for it is confined to Europe and Siberia 

 and IS probably the summit of a long line of descent. Like Corallorhi^a it is really 

 a subterranean plant, mcreasing underground by runners, sometimes for several years 

 and only throwmg up a flower-spike in favourable seasons to renew the vigour of 

 the species by cross-pollination. It is the earliest example in the European flora of 

 an empty spur with liquid stored between its walls. 



We now come to the Ophrydeas in which evolution has made enormous strides. 

 The hitherto simple rostellum" now develops into a separate viscidium for each 



' Darwin thought that the single viscidium was arrived at by the cohesion of two separate viscidia 

 which IS the case in Aceras, and perhaps in Hl„,antoglossun,. ^But as we have s^^the rSum is 



