518 



THE DICTIONARY OF GARDENING, 



Orchid Fertilisation continued 



labellum have reversed the positions they occupy in the 

 other forms. In the large group of Epidendrece, of which 

 so many are cultivated in hot-houses, the adaptations for 

 cross-fertilisation, though less complex than in Catasetum, 

 well deserve a short notice. Cattleya is selected as an 

 easily-obtained type ; but Lcelia, Chysis, and other genera, 

 only differ from Cattleya in minor details. The positions 

 of the labellum and of the column will be readily made 



Fio. 766. CATTLEYA TRIAN.E. 



out (see Figs. 762, 765, and 766). The column is promi- 

 nent, and arches forward, having the stigmas on the front 

 or lower surface, near the tip. Just beyond them is the 

 rostellum, the lower surface of which is thickly covered 

 with sticky liquid. Beyond this, again, on the tip, is 

 the anther. The pollen grains are joined to form four 

 chief masses, which end in caudicles, to which many 

 separate small groups, each of four grains, are stuck. 

 The caudicles have no disks ; they lie so that their 

 tips are on the dry, membranous, upper surface of the 

 rostellum. The labellum usually has the sides folded up 

 so as to nearly surround the column. The nectary is a 

 narrow tube between the labellum and the base of the 

 column in front. "When an insect of suitable size comes 

 to suck the nectar, it must push its way between the 

 labellum and the front, or lower, surface of the column ; 



Orchid Fertilisation continued. 



and must get well in below the latter before reaching 

 the nectar. In doing this, its back presses against the 

 stigmas, and leaves on them pollen from any previously 

 visited flower. In retreating, the insect presses its back 

 against the lower surface of the rostellum, and becomes 

 smeared with the fluid, some of which is also forced on 

 to the caudicles, and causes them to stick to the insect; 

 and the pollinia are thus drawn out and fixed to it, to 

 be transferred to the next flower visited. It will be 

 observed that the method of affixing the pollinia in these 

 plants reminds us a little of that previously described as 

 occurring in Listera ovata ; but the larger size renders it 

 more easy to study the process iu Cattleya and its allies, 

 and the differences in details are sufficiently obvious. 



Some Orchids are now so specialised to adapt them- 

 selves for cross-fertilisation alone, that the stigma dies 

 (as if poisoned) when pollen from the same 

 flower is placed on it; e.g., species of Bur- 

 lingtonia and of Oncidium. Between this 

 extreme and habitual self-fertilisation in 

 cleistogamic flowers, every stage is to be 

 encountered. In many cases, where me- 

 chanical obstacles prevent the pollen of a 

 flower being transferred to its stigma, the 

 ovules are well fertilised (e.g., in Orchis 

 maculata) if pollen is placed on the stigma 

 of the same flower. 



An interesting example of the way in which 

 an Orchid, possessed of structures intelli- 

 gible in their origin only as suited to cross- 

 fertilisation, is converted by a slight altera- 

 tion, so as to enable its ovules to be fer- 

 tilised by pollen of the same flower, is well 

 seen in the Bee Orchis (Ophrys apifera). 

 In this plant, the parts are, in many respects, similar 

 to those of Orchis maculata ; but the pollinia have long, 

 slender, flexible stalks, and the mass of grains in each 

 slips out of the pouch of membrane, and hangs in front 

 of the stigma, retained by the disk, and the slightest 

 swaying movement causes it to strike against the stigma, 

 and to leave pollen on it. The flower is not much, if 

 at all, visited by insects, and it possesses no attractions 

 for them. 



A striking anomaly is that observed by Dr. P. Miiller, 

 in South Brazil, in which an Epidendrum possessed two 

 lateral stamens that secured self-fertilisation, and a 

 median one, from which the pollen could be removed 

 only by insect or other extraneous aid. The rarity with 

 which this is effected, is indicated by the absence of 

 attractions for insects in the flower. A considerable 

 number of self -fertilised Orchids have been put on 

 record. One of the latest papers on this subject is 

 entitled, " On the Contrivances for Insuring Self -Fertili- 

 sation in some Tropical Orchids," by Henry 0. Forbes, 

 in the "Journal of the Linnean Society," vol. xxi., 

 pp. 538-49, tt. 16 & 17. 



ORCHID HOUSE. This term is applied to any 

 garden structure in which Orchids are cultivated, to the 

 exclusion of all, or nearly all, plants of another descrip- 

 tion. It is not necessary, nor, indeed, always thought 

 advisable, to relegate these plants to certain houses by 

 themselves ; but in nurseries, where space for thousands 

 of living imported specimens have frequently to be 

 found, and a large collection of established plants is 

 also grown, not only are special Orchid Houses found 

 necessary, but large structures are frequently devoted 

 wholly to the accommodation of such genera as Cattleya 

 or Odontoglossum alone. Nor is this system entirely 

 limited to nurseries ; many private collections have now 

 become so extensive, in consequence of the frequent 

 additions made, that similar arrangements are being 

 adopted. Where large and varied collections of Orchids 

 are grown, they are usually arranged, according to the 



