THE FRUIT AND SEED-DISPERSAL 



•80 



Dissemination by Wind and \Vati:r. 



More frequently the motor impulse is from witliout, tlic chief 

 agents being wind, water or some moving animal. Wind acts ch'r'-rth.- 

 upon small seeds, such as those of Orchids, 

 scattering them as it would so much dust. 

 It may act less directly where the seeds are 

 larger, and the dehiscent fruit is borne on 

 a stiff stalk, as in the gaping follicles of 

 the Aconite, which, shaken by the wind, 

 scatter their seeds all round the parent 

 (Fig. 227) : or in the Poppy (Fig. 231) or 

 Canterbury Bell, which do the same; but 

 here the dehiscence is by pores, the prin- 

 ciple being that of the Pepper-Box. 



The wind would no doubt influence the 

 fall of any seeds ; but the development 

 upon them of tufts of hair, or of broad 

 thin wing-like surfaces, enhances its effect 

 upon their transfer, even where the seeds 

 are relatively large. Such developments 

 are sometimes upon the seed itself, as in the 

 case of dehiscent fruits : or they may be 

 formed by the carpellary walls where the 

 fruit is one-seeded, or where it breaks into 

 one-seeded parts. The development of hairs on the seeds themselves 

 is seen in the Willow and Poplar, in Cotton (Fig. 232), and in the 



Fig. 231. 

 Capsule of Poppy opening by 

 pores below the star-shape<l 



stigma. (After Fif;uit'r.) 



Fig. 232. 

 Seed of Cotton with superficial hairs. 

 (After Figuier.) 



Fig. 23,^ 



Fruit of Valerian. 



Figuier.) 



(.After 



Willow-herb. When in any of these the fruit splits, the seeds arc set 

 free, each with its hairy parachute, which supports it in tiie breeze, 



