102 THE FRUIT : DISPERSAL OF SEEDS 



In the kidney-vetch (p. 432) the calyx is large, thin, and 

 inflated, and in some species of clover the faded corolla is large 

 and of small weight in comparison with the single-seeded pod 

 which it encloses. 



The perianth in many docks developes into thin wing-like 

 projections surrounding the fruit, and winged extensions of the 

 pericarp are seen in the ash, sycamore, elm, and certain um- 

 belliferous plants. Some of these fruits are of such weight that 

 they fall almost vertically when allowed to do so, although 

 with a slow spinning motion. They are, however, only de- 

 tached by strong winds or gales, and under these circum- 

 stances, may be carried considerable distances. Not only are 

 the external parts of the pericarp and other portions of the 

 flower modified for wind distribution, but the seeds themselves 

 of many dehiscent fruits show similar adaptations to the same 

 end. In the willow, poplar, willow-herb {Epilobium), and 

 cotton, the testa is more or less covered with long, silky, 

 buoyant hairs, and many seeds, such as tulip and yellow rattle 

 (p. 608), have thin, wing-like membraneous margins. 



In the hop, and most grasses, the buoyant agents are the 

 bracts surrounding the fruit. 



Water-plants have fruits and seeds, the bracts of which enclose 

 more or less air which enables them to float some distance. 



A large number of seeds are spread over the earth by animal 

 agency. Upon the pericarp of the carrot, hedge-parsley {Torilis), 

 and other umbelliferous plants, and also that of cleavers {Galium 

 aparine), and many medicks, spinous and hook-like structures 

 are present, which cling to the fur, wool and feathers of animals. 

 Similar hook-like projections are seen also on the receptacle of 

 agrimony and on the involucral bracts of the common burdock 

 {Arctium Lappa L.). Eventually the fruits are rubbed off or fall 

 off the animal's coat in another locality from that in which they 

 were collected ; in this manner seeds may be transported long 

 distances. 



