388 



PRACTICAL BOTANY 



insect-catching powers stand a far better chance to exist as 

 air plants, or in the thin, watery soil of bogs than ordinary 

 plants which have no such habits. 



359. Irritability in plants. 1 The popular notion of what 

 plants can do does not credit them with any power to execute 

 movements. It is true most people have heard of sensitive 

 plants, which fold up their leaflets when touched. Every one 



who is very observant must 

 have noticed such move- 

 ments as those of bean, 

 clover, and other leaves in 

 taking the nocturnal posi- 

 tion (Figs. 52-54). 



Even people who are not 

 botanists are usually much 

 impressed when they see for 

 the first time such prompt 

 and apparently purposeful 

 movements as those by 

 which the stamens of the 

 barberry flower spring up 

 upon being touched, or 

 those by which the Venus's- 

 flytrap catches insects. But 

 in general the movements 

 of plants are executed so 

 slowly that the change of 

 position of the plant as a whole, or of its parts, can only be 

 discerned by magnifying the motion in some way or by noting 

 the successive positions occupied at considerable intervals of 

 time. And yet plants do move so generally that in comparing 

 them with animals we can only say that " most animals are 

 more active than most plants." 



All of the actions of plants are due to the irritability of 

 their protoplasts. By this is meant simply their power of 

 1 See Coulter, Barnes, and Cowles, Textbook of Botany, Vol. I, chap. v. 



FIG. 315. Venus's-flytrap 



