90 AKETHUSE^. Chap. Ill 



Mr. Fitzgerald describes and figures several other 

 genera, and states with respect to Acianthus fornicatus 

 and exsertus that neither species produce seeds if 

 protected from insects, but are easily fertilised by 

 pollen placed on their stigmas. Mr. Cheeseman * has 

 witnessed the fertilisation of Acianthus sinclairii in 

 New Zealand, the flowers of which are incessantly 

 visited by Diptera, without whose aid the pollinia are 

 never removed. Out of eighty-seven flowers borne 

 by fourteen plants, no less than seventy-one matured 

 capsules. This plant according to the same observer 

 exhibits one remarkable peculiarity, namely, that the 

 pollen-masses are attached to the rostellum by means 

 of the exserted pollen-tubes, which serve as a caudicle ; 

 and the pollen-masses are thus removed together with 

 the rostellum, which is viscid, when the flowers are 

 visited by insects. The flowers of the allied Cyrto- 

 stylis are also much frequented by insects, but the 

 pollinia are not so regularly removed as those of the 

 Acianthus ; and with Corysanthes, only five out of 200 

 flowers produced capsules. 



The Vanillidse according to Lindley form a sub- 

 tribe of the Arethusese. The large tubular flowers of 

 Vanilla aromatica are manifestly adapted to be ferti- 

 lised by insects ; and it is known that when this plant 

 is cultivated in foreign countries, for instance in Bour- 

 bon, Tahiti, and the East Indies, it fails to produce 

 its aromatic pods unless artificially fertilised. This 

 fact shows that some insect in its American home is 

 specially adapted for the work ; and that the insects 

 of the above-named tropical regions, where the Yanilla 

 flourishes, either do not visit the flowers, though they 

 secrete an abundance of nectar, or do not visit them 



* ' Transact. New Zealand Institute,* vol. vii. 1875, p. 843. 



