How Plants Secure Change of Location 385 



capsules on long stiff-elastic stalks. When the stalks are shaken 

 by gusts of wind, or the impact of animals passing, the seeds are 

 thrown out by the movement, especially the jerky recoil. The 

 exit of the seeds from some of these pods lies along smooth 

 grooves so placed as to 

 guide the seeds at an 

 angle best for their flight 

 to a distance. These fea- 

 tures appear well in the 

 Poppies (figure 154), 

 upon which observation 

 and experiment are easy ; 

 but it really is one of the 

 commonest of the modes 

 of dissemination, prevail- 

 ing through several large 

 families of plants, nota- 

 bly the Figworts, Bell- 

 worts, Primroses and 



Pinks. And Other meth- FIG. 151. The pods of Acanthus explosively pro- 



ods of projection occur, 



as the reader may see for himself in the field, or find described in 



the works on the subject. 



A special form of projection through movements of ripening 

 tissues is shown by those seeds which are pushed along the ground 

 by movements of hygroscopic hairs. The causes of hygroscopic 

 movements were considered in the chapter on Absorption; and 

 it will here suffice to say that some tissues, by absorbing moisture 

 from the air, or giving it up thereto, can swell and twist very 

 forcibly, though not suddenly. In some Clovers hygroscopic 

 hairs are so placed in conjunction with backwardly-directed 

 parts, which act as "chocks," that every movement of the hairs 

 pushes the seed along the ground (figure 155). The arrangement 

 is yet better in the curious "living Oat" (Avena sterilis}, which can 



