86 AKETHUSE.E. Chap. UI. 



Cephalanthera offers only a partial exception to the 

 rule that the flowers of Orchids are generally fertilised 

 by pollen from another plant. 



Gephalanthera ensifolia. — According to Delpino,*the 

 flowers of this species are visited by insects, as shown 

 by the removal of the pollen-masses. He believes that 

 this is effected by their bodies being first rendered sticky 

 by means of the stigmatic Secretion. It is not clear 

 whether the flowers also fertilise themselves. Each 

 pollen-mass is divided into two, instead of being merely 

 sub-divided, so that there are four distinct pollen-masses. 



Pogonia opMoglossoides. — The flowers of this plant, 

 an inhabitant of the United States, resemble, as 

 described by Mr. Scudder, f those of Cephalanthera in 

 not having a rostellum, and in the pollen-masses not 

 being furnished with caudicles. The pollen consists of 

 powdery grains not united by threads. Self-fertilisation 

 seems to be effectually prevented ; and the flowers on 

 distinct plants must intercross, for each plant generally 

 bears only a single flower. 



Pterostylis trullifolia and longifolia. — I may here 

 briefly mention some Orchids, inhabitants of Australia 

 and New Zealand, which are included by Lindley in 

 the same family of the Arethusese with Cephalanthera 

 and Pogonia, and are remarkable from their labella 

 being extremely sensitive or irritable. Two of the 

 petals and one of the sepals form a hood which encloses 

 the column, as may be seen at A in the accompanying 

 figure of Pterostylis longifolia. 



The distal portion of the labellum affords a landing- 

 place for insects, in nearly the same manner as with 

 Cephalanthera; but when this organ is touched it 

 rapidly springs up, carrying with it the touching insect, 



* 'Ult. Oeservaz. sulla Dico- t ' Pro"- Boston Soo. Nat. Hist, 



garaia,' part ii. 1875, p. 140. vol. ix. 1863, p. 182. 



