PALM HOUSE 117 



the peculiar properties of that plant, the name of which he 

 has immortalised as the title of perhaps the most glowing 

 description of a flower-garden in our literature*; or, again 

 that the same interesting plant was made the subject of a 

 pictorial simile by A. C. Collins in the beautiful picture 

 " Convent Thoughts," in the University Galleries. On being 

 touched gently, the paired leaflets close upward. On rougher 

 treatment the pinnae fold, and eventually the whole leaf sinks 

 down and hangs as if withered. But after an interval the 

 leaves rise and the leaflets open once more. 



Equally wonderful, though in quite a different way, is the 

 Acacia sphaerocephala. It is provided with organs by which, 

 in a state of nature, it is enabled to keep a mercenary army, 

 an army of ants, for its own protection. The large stipular 

 thorns are hollow, and serve as sentry-boxes or dwelling- 

 places for the ants, which are thus not only housed, but are 

 also fed by the plant, on Belt's corpuscles, ovoid structures, 

 rich in proteids, which are developed at the ends of the 

 leaflets, and are so loosely attached as to be easily plucked 

 by the hungry soldiers. Similar food-bodies are grown by 

 the Imbauba or Trumpet Tree (Cecropia), and by Thunbergia, 

 plants belonging to totally different natural orders, but having 

 similar close relations with protective ants. 



Amongst the shrubs or trees which have been grown on 

 account of the valuable articles of commerce they yield, we 

 may mention the following plants : 



Coffee, the seeds of Coffea liberica (or C. arabicd)^ now 

 grown in many tropical countries. Our total imports exceed 

 ,2,500,000 in value and 46,000 tons in weight. One of 

 the earlier papers of Dillenius, written before he came to 

 Oxford, was " De Cahve arabico." 



Cocoa or chocolate comes from a small neotropical tree, 



* "The Sensitive Plant." was written in the garden of Lady Mount- 

 cashell, less than ten years after Shelley 'had been sent down from 

 Oxford. 



