ORCHIDACEAE 469 



in Drymoda and others, the labellum and the sepals on either side of 

 it are carried forward on an axial protuberance in such a way that the 

 sepals appear to spring from the labellum, the axial growth (ckin) 

 appearing like the basal part of this organ. Some of these construc- 

 tions are very complex. Several are described in connection with 

 the genera to which they belong. 



Similarly the column shows great variety in structure (refer as 

 above). One point may be mentioned specially as of importance in 

 classification. In the simple case of Orchis, &c., described above, the 

 base of the anther loculi is against the rostellum ; such cases are called 

 basitonic; in others it is the apex that is next the rostellum (Oncidium, 

 &c.), and these are acrotonic. 



[Diandrae. So far only monandrous forms have been con- 

 sidered. In Cypripedium and its allies the column has i anthers, no 

 rostellum, and a simple stigma, composed of the 3 carpellary stigmas. 

 The two sta. belong to the inner whorl, and the sta. which in 

 Monandrae is fertile, is here repres. by a large std. The stigma is 

 not sticky, but the pollen is, and it is not combined into pollinia.] 



The ovary is inf. in all O., uniloc. with 3 parietal plac. (exc. 

 Apostasia), and oo ovules, which do not develope until fert. of the fl. 

 occurs. 



The adaptations of orchid flowers to fertilisation by insects are 

 endless, and many very complicated. Reference must be made to 

 text-books for the details. No student should omit to read Darwin's 

 Fertilisation of Orchids, at least the first two and the last chapters. 

 In it will be found accounts of the mech. of most of the common gen. 

 A few general points only can be mentioned here ; in the description 

 of the individual gen. other details are given. Very few secrete free 

 honey ; in most cases the insect has to bite into or drill the tissue for 

 the juice therein contained ; this tissue is usu. part of the labellum 

 often a spur at the base or the basal part of the column. The 

 pollinia are removed as a rule when the insect is going out of the fl. 

 In most cases the insect in entering displaces the rostellum or some 

 portion of it, and thereby exposes and comes into contact with a 

 sticky mass (due to disorganisation of cells formerly living). This 

 becomes cemented to the insect while it is drilling for honey, and as 

 the insect goes out again it takes, with it the viscid lump, together 

 with the pollinia, either merely glued to it, or attached by caudicles. 

 In many cases the pollinia are in such a position that when the insect 

 enters the next fl. they will touch the stigmas. In others this is not 

 so, e.g. Orchis, where the anthers and stigma are far apart on the 

 column, and in such cases the pollinia, on getting out of the anther, 

 execute a hygroscopic movement which brings them into the proper 

 position on the insect's body to strike the stigmas. Such is the 

 general principle of the orchid mechanism, but the variety in detail 

 is endless. Many fls. have the most extraordinary structure, e.g. 

 Coryanthes, Stanhopea, Vanda, &c. See under gen. 



The fruit is a caps., containing usu. a gigantic number of ex- 

 ceedingly small and light seeds, which are well suited to wind distr. 

 (hence, among other causes, the epiph. habit of so many). 



The O. are favourites in horticulture, and very many gen. are cult. 



