88 ENGLISH BOTAXY 



and in clefts of trees, procuring their nourislimcnt partly from the atmosphere, and 

 partly from the decaj-ing organic matter that casually accumulates about their roots. 

 To denote this mode of existence, and to distinguish them from " parasites," the tree- 

 inhabiting orchids are called "epiphytes." No plants unfold blossoms of more 

 fantastic beauty, or of odours more delicious, or colours more vivid. They are 

 utterly unlike other plants, and seem to take pleasure in the widest possible diver- 

 gence from all accustomed types of structure, especially in the flowers, which remind 

 us of insects, birds, reptOes, and even the human figure. Several of these vegetable 

 mimics reside in our own country, but the .species are distributed all over the globe ; 

 the largest number are, however, found in the tropics. In temperate countries — where 

 they are exclusively terrestrial — they ornament groves, meadows, and marshes with 

 flowers like httle hyacinths. In the hot damp woods of the equatorial regions they are 

 chiefly aerial, decorating the trees with the highest splendours of natural jeweller}-. 

 Our great naturalist, Mr. Darwin, has written extensively on the nature and structure 

 of orchids. He shows that most, if not all, of the British species require the aid of 

 insects in order that the ovules may be fertilised — in other words, that an orcliid is 

 incapable of producing ripe seed by vii'tue merely of its own powers, and that the 

 structure is actually opposed to it, and that were moths and other insects not to visit 

 these plants when in bloom, they would be sterile. Moths he calls their " mamage 

 pi'iests." Deviations the most extraordinary from the customary condition and size 

 of the parts appear to form no exception to the rule. If the flower be so constnicted 

 as to require some special adaptation on the part of an insect, the insect is forth- 

 coming. The means by which the operation of fertilisation is performed has been 

 minutely described by Mr. Darwin, and his work " On the Fertilisation of Orchids " 

 is illustrated with numerous engravings, which greatly assist his readers to under- 

 stand his theory. He says, '' Let us suppose an insect to alight on the labellum, 

 which forms a good landing-place, and to push its head into the chamber at the back 

 of wliich lies the stigma, in order to reach with its proboscis the end of the nectary ; 

 or, which does equally well to show the action, push a sharply-pointed common pencQ 

 into the nectary. Owing to the pouch-formed rostellum projecting into the gangway 

 of the nectary, it is scarcely possible that any object can be pushed into it without 

 the rostellum being touched. The exterior membrane of the rostellum then ruptures 

 in the proper lines, and the lip or pouch is most easily depressed. When this is 

 effected, one or both of the viscid balls which lie at the base of the rostellum will 

 almost infallibly touch the intniding body. So viscid are these balls that whatever 

 they touch they firmly stick to. Moreover the viscid matter has the peculiar chemical 

 quality of setting, like a cement, hard and dry in a few minutes' time. As the anther- 

 cells are open in front, when the insect withdi-aws its head, or when the pencil is 

 withdrawn, one pollen-bag or both will be withdrawn firmly cemented to the object 

 projecting up like horns. The firmness of the attachment of the cement is very 

 necessary, as we shall immediately see ; for if the pollen-bags were to fall sideways or 

 back^vards they could never fertilise the flower. From the position in which the two 

 poUinia lie in their cells, they diverge a little when attached to any object. Now, let 

 us suppose our insect to fly to another flower, or insert the pencil with the attached 

 pollen-bag into the same or into another nectai-y, it will be evident that the firmly- 

 attached pollen-bag will be simply pushed against or into its old position — namely, 

 into its anther-cell. How then can the flower be fertilised ? This is effected by a 

 beautiful contrivance : though the viscid substance remains immovably fixed, the 

 apparently insignificant and minute disc of membrane to which the caudicule adheres 

 is endowed with a remarkable power of contraction, which causes the pollen- bag to 



