GYNANDRJ1. 333 



ascending shoots, which bear the foliage-leaves, may vary, but they very often 

 swell and assume the form of a tuber, which persists for several years fresh 

 and green after the leaves have fallen off (Fig. 321). Vanilla is an exception 

 (see above). Our Orchids are all terrestrial (or marsh-plants) ; the largest 

 number of species is found in calcareous soils. 



POLLINATION takes place principally by means of insects, but self-pollina- 

 tion occurs in some. The lip serves as a landing-stage for the insect visitors, 

 which, on sucking the honey, cause the adhesive discs, with the pollinia 

 attached to them, to adhere to their bodies (generally to the probosces) and so 

 carry them away to other flowers. In some species parts of the flower are 

 sensitive or irritable, which has some connection with the pollination. 

 Without doubt there are a great many biological differences which are closely 

 connected with the infinite multiplicity of forms ; Darwin (1862) has already 



FiQ. 321. Chysia bractescens. 



shown an enormous variety, never even dreamt of before, in the European 

 species. The genus Catasetum has $ - ? - and $ -plants with flowers of such 

 different appearances that they have been classed in various genera (Myanthus, 

 Monacanthus). Platanthera is pollinated by hawk-moths ; Ophrys, by flies ; 

 Epipactis latifolia, by wasps ; Orchis, by bees, especially humble-bees, etc. 



The DISTRIBUTION OF SEEDS is effected by the wind, the seeds being so ex- 

 ceedingly small and light. Many species moreover have peculiar, elater-like, 

 fine, hygroscopic hairs in the ovary, which eject the seeds in a manner similar 

 to the elaters of the Liverworts. , 



The USES are few, mostly as ornamental plants in conservatories. The 

 tubers of several Orcfa's-species are OFFICINAL ; they contain starch and mu- 

 cilage and are used as " salep." The fruits of Vanilla planifolia are used as 

 condiments and differ from other Orchid-fruits in being rather fleshy and 

 in dehiscing irregularly ; the seeds are very small, shining and black. 



