358 



NATURE 



\Feb. 2 2, 1877 



" epichil," or upper part of the labellum, fits closely to 

 the column and is very stiff and elastic. The first bee 

 which is immersed will have the pollinia glued to its back 

 by their viscid disc. Having escaped through the passage 

 with this appendage, the insect then returns nearly im- 

 mediately to its feast, when it is generally precipitated a 

 second time into the bucket, passes out through the same 

 opening, and thus inserts the pollinia into the stigma as 

 it forces its way out, thereby impregnating either the 

 same or some other flowers. Dr. Criiger states that he 

 has seen so many of the bees taking part in this opera- 

 tion that there is a continual procession of them through 

 the passage. " There cannot be the least doubt," says 

 Mr. Darwin, " that the fertilisation of the flower absolutely 

 depends on insects crawling out through the passage 

 formed by the extremity of the labellum and the over- 



FiG. 2. — Coryfintkes speciosa (after Lindley). L, labellum ; b, bucket of 

 labellum ; H, fluid-secreting appendages ; p, spout of bucket, over-arched 

 by the end of the column bearing the anther and stigma. 



arching column. If the large distal portion of the 

 labellum or bucket had been dry the bees could easily 

 have escaped by flying away. Therefore we must believe 

 that the fluid is secreted by the appendages in such 

 extraordinary quantity, and is collected in by the bucket, 

 not as a palatable attraction for the bees, as these are 

 known to gnaw the labellum, but for the sake of wetting 

 their wings and thus compelling them to crawl out 

 through the passage." 



3. Catasetutn saccattim. — The genus Catasetum belongs 

 also to the sub-order VandccC, and to a section of that 

 order, the Catasetidas, distinguished from all other orchids 

 by several very remarkable peculiarities. In the first place 

 it stands almost alone among all genera of orchids in 

 having unisexual flowers ; and so greatly do the male and 

 female flowers— which are usually borne on different 

 plants— differ from one another, that they were long 



regarded as belonging to different species, or even genera ; 

 while, to complicate the matter still further, some kinds 

 have a third hermaphrodite form differing greatly from 

 either of the others. Thus Catasetum trideittatuni (male), 

 Monachanthus viridis (female), and Myanthus bai'batus 

 (hermaphrodite), are now known to be three forms of the 

 same species. The second peculiarity of the male flowers 

 of Catasetutn is that they are provided with an extraordi- 

 nary mechanical contrivance by means of which the pol- 

 linia are forcibly ejected on to the back of the insect, and 

 thus carried to a female flower of the same species. 

 There is no nectar in the male flower to attract insects ; 

 the ejection of the pollinia results from the accidental 



Fig. ^.— Catasetum saccatum. a, front view of column; b, side view of 

 flower, with all the jjerianth except the labellum rernoved ; a, anther : 

 an, antennae ; d, viscid disc ; /, labellum ; fd, pedicel cf pollinium : 

 f, stigmatic chamber. 



touching, by the wing of a passing insect or of one seated 

 on the labellum for the purpose of gnawing it, of two long 

 horns or antenncE, which occur in no other genus, and are 

 placed in such a position that when touched by the insect 

 the pollinia are projected on to its body, to which they 

 adhere by their blunt and excessively adhesive point. 

 The insect then flies away to a female plant, and while 

 standing in the same position as before on the flower, the 

 pollen-bearing end of the pollinia is inserted into the stig- 

 matic cavity, and a mass of pollen left on its viscid disc. 

 Mr. Darwin has examined five species of Catasetum, and. 

 finds that this is the only possible way in which they can 

 be fertilised. 



In the accompanying Fig. 3 (a being a froat, B a side 



