HYGROSCOPIC AND TURGOR MOVEMENTS 411 



touch or breath of wind is sufficient to Uberate them. When 

 this happens each valve rolls up inwards like a watch-spring, 

 with great violence, and in doing so whips out the seeds 

 which fly to some distance. In the famous squirting 

 cucumber of Italy, Echallium Elaterium, the internal turgor 

 pressure extends the outer wall of the fruit ; at a certain 

 point the stalk end is forced out, exactly like the cork of a 

 champagne bottle, the fruit wall contracts, and the whole 

 juicy contents including the seeds are squirted out. 



Another type of movement, hygroscopic in nature, is 

 exhibited by the awns of Geranium, Erodium, and of some 

 grasses. The awn is derived from the style, which spHts 

 off in five strips from a central column. Each awn has 

 attached to its base a bit of the ovarial wall partly enclosing 

 a single seed. The Erodium awn on drying twists into a 

 spiral, that of Geranium curls up ; on wetting they straighten 

 out. These movements may be repeated indefinitely. 

 They have been interpreted in two ways — as enabling the 

 seed to " crawl " slowly over the ground, and as ensuring 

 that it shall be pushed into some crack and so buried. 



Dispersal by External Agency. — Three agencies may be 

 efi"ective — animals, the wind, and water currents. 



A. Animal transport may be external or internal. In 

 either case it gives the possibility of wide and rapid dispersal. 

 Very evident is the animal relation to those fleshy fruits 

 which are eaten by birds and mammals. The edible part 

 may be the fruit wall or may be an aril, as in the fleshy cup 

 of the yew, or the mace of the nutmeg, which is eaten by 

 pigeons. We may note the frequent occurrence of red in 

 the colouring as related to the fact that mammal and bird 

 both see this in sharp contrast to green. An important 

 point in internal transport is the resistance of the seed to 

 digestion. The kernels of stone fruits must be very 

 resistant both to mastication and digestion, but seeds which 

 seem much less well protected may pass unharmed through 

 the digestive tract, as is the case with those of the tomato 

 or gooseberry. Of course successful resistance depends not 

 only on the seed or fruit, but on the type of animal which 



