Chap. IX. LINES OF DESCENT. 263 



is a related genus, placed by Brown amongst the 

 Orchidese, but by Lindley in a small distinct family. 

 These broken groups do not indicate to us the structure 

 of the common parent-form of all the Orchidese, but 

 they serye to show the probable state of the order in 

 ancient times, when none of the forms had become so 

 widely differentiated from one another and from other 

 plants, as are the existing Orchids, especially the 

 Vandese and Ophreae ; and when, consequently, the 

 order made a nearer approach in all its characters, 

 than it does at present, to such allied groups as the 

 Marantacese. 



With respect to other Orchids, we can see that an 

 ancient form, like one of the sub-tribe of the Pleuro- 

 thallidse, some of which have waxy pollen-masses with 

 a minute caudicle, might have given rise, by the entire 

 abortion *of the caudicle, to the Dendrobiae, and by an 

 increase of the caudicle to the Epidendreae. Cymbi- 

 dium shows us how simply a form like one of our 

 present Epidendrese could be modified into one of the 

 Vandese. The ISTeottese stand in nearly a similar relation 

 to the higher Ophrese, which the Epidendrese do to the 

 higher Vandese. In certain genera of the Neottese we 

 have compound pollen-grains cemented into packets 

 and tied together by elastic threads, which project and 

 thus form a nascent caudicle. But this caudicle does 

 not protude from the lower end of the pollinium as in 

 the Ophrese, nor does it always protrude from the ex- 

 treme upper end in the NeottcEe, but sometimes at an 

 intermediate level ; so that a transition in this respect 

 is far from impossible. In Spiranthes, the back of the 

 rostellum, lined with viscid matter, is alone removed : 

 the front part is membranous, and ruptures like the 

 pouch-formed rostellum of the Ophrese. An ancient 

 form combining most of the characters, but in a less 



