32 6 BOTANY OF THE LIVING PLANT 



so that it may be conveyed to a distance before reaching the ground. 

 In many Valerianaceae (Fig. 246) and Compositae (Fig. 247), where 



< 



the fruit is one-seeded and does not 

 split, the calyx is persistent, and 

 developing as the feathery pappus 

 buoys up the inferior achene when 

 set free, so that it may be conveyed 

 to a distance before reaching the 

 ground. The development of flat- 

 tened wings upon seeds or fruits is 

 closely analogous. Examples in 

 the case of winged seeds are seen 

 in the Bignoniaceae (Fig. 248), and 

 of winged fruits in the Elm, Ash 

 or Sycamore (Fig. 249). It is note- 

 worthy that winged seeds and fruits 

 are most common where the plants 

 that bear them are of some stature, 

 or are climbers ; so that they have 

 to fall a considerable distance. The 

 wind has thus a chance of scatter- 

 ing them far and wide. 



For large seeds a more effective 

 means of transit is by water, which 

 in commerce is a very efficient 

 method for goods generally. Given 



a movement of water and a floating seed or fruit, dispersal is easy. 



The Water Lily is an example. The large berry ripens under water. 



It there splits, and the coherent mass of seeds, each with bubbles 



held in its aril, floats to the surface. 



There the seeds separate, drifting 



about till the bubbles are liberated 



by the decay of the aril. The seeds 



thus dispersed then sink. More 



striking examples are seen in lit- 

 toral or estuarine plants, of which 



the seeds or fruits are often very 



large : for provided they float the 



size is immaterial. In Barringtonia 



(Myrtaceae), Scaevola (Goodeniaceae), and Heritiera (Sterculiaceae), 



which are all estuarine plants, the relatively large fruits have a fibrous 



Fig. 247. 



Fruit of Dandelion, with pappus as 

 parachute. Note the absence of bracteoles 

 on the general receptacle. 



Fig. 248. 



Winged seed of one of the Bignoniaceae. 

 (Reduced.) 



