90 ARETHUSE^. Chap. III. 



Mr. Fitzgerald describes and figures several other 

 genera, and states with respect to Acianthus fornicatus 

 and emsertus 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 aUied 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 

 fiowers 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, 349. 



