52 PLANT LIFE. 



hygrometrica in Queensland, and another in North 

 America, the Porcupine Grass {Stipa sparted). The 

 ordinary function of these twisting awns is, of course, to 

 bury the seed in the ground ; the process is easily 

 shown if the dry fruit of Avena sterilis is placed in 

 a drop of water on a table. It will also show the 

 peculiar motion when left to dry. 



Not very many plants show special adaptations to 

 water transport, although most of those which grow in 

 water or marshy places float easily in consequence of the 

 numerous air cavities in their tissues. Hence any part 

 broken off may carry the fruit a long distance. In the 

 White Water-lily each seed has a small envelope^ or 

 " arill' which is full of air cavities of this kind, so that 

 the seed can float for a short time. In the Yellow Water- 

 lily {Nuphar) the carpels themselves float The Cocoa- 

 nut is a well-known example of a floating fruit : the 

 nut itself or shell is really the inner lining of the carpels. 

 The middle part of the carpels has become a mass of 

 light fibrous material, " coir," much used in brush- 

 making. The outer layer of the carpel is a thin white 

 skin which covers the whole fruit. It is therefore very 

 buoyant and can float for a very long time. As a 

 matter of fact, even quite recently formed atolls in the 

 Pacific soon become inhabited by cocoanuts, whose 

 fruits have drifted to them. 



The table here given shows how very varied are the 

 parts of the fruit or seeds which are utilised for 

 transport. 



It is impossible to explain one difficulty brought out 

 very clearly by this table, namely, how these specialised 

 arrangements come to be formed exactly where they 

 are required. Why should the awn of several grasses, 

 and the carpel of the Meadow Crane-bill become hygro- 



