MIMOSA 55 



cies and may be easily observed in the bean, 

 oxalis, locust, cassia, and other leguminous 

 species. 



It has other forms of irritability, not at all 

 common or widely distributed. Thus if one 

 should lightly touch, or blow the breath upon, 

 the expanded leaflets of mimosa at ordinary 

 temperatures, the pinnules or ultimate divi- 

 sions of the leaf would rise up above the mid- 

 ribs upon which they are borne, closing in 

 pairs. If the shock were given with sufficient 

 force or if a blow of the pencil be given u])on 

 the stem all the leaves will erect the pinnules 

 and sink on the petioles. A flame held near 

 the leaflet, or the fumes of acid, ammonia, or 

 chloroform, will cause the movement also, 

 while an electric current applied to almost 

 any part of the plant has a similar effect. 

 More correctly speaking, the breaking of the 

 current is the true stimulus. The plant re- 

 sponds to chemical, mechanical, thermal 

 and electrical stimuli. An interesting differ- 

 ence between the reactions of mimosa and 

 those of the tendrils of climbing plants is that 

 the latter move when pressed by a solid body, 

 but not when struck. Mimosa, on the other 

 hand, responds to a blow or shock, but not to 

 a steady pressure, as the leaves may be given 

 a steady pressure by the thumb and finger 

 without results. 



