264 



THE LIFE OF THE PLANT 



leaves of the sensitive mimosa, which grows in our 

 greenhouses. It is curious to witness the amazement 

 of a person who has never before heard of this 

 plant, and sees for the first time the way it folds its 

 leaves on being slightly disturbed. It is only then 

 that we realise how deeply rooted is the conviction, 

 based as it is upon daily experience, that motion is 

 not a characteristic of plants. Normally, the leaf of 

 the mimosa has the appearance shown in fig. 77 on the 



FIG. 77 



right-hand side. This is a so-called compound leaf. 

 Its main leaf-stalk bears four stalks spread out like 

 a fan, and each of these in its turn bears a con- 

 siderable number of leaflets distributed in pairs. We 

 have only to touch such a leaf or irritate it in some 

 way and it will move. The leaflets will raise them- 

 selves in pairs, and fold like the wings of a butterfly 

 at rest. The four spreading stalks will lay them- 

 selves together, and the main leaf-stalk will eventually 

 droop, and sink downwards. The whole plant will 

 look like the leaf on the left-hand side of fig. 77. 

 The higher the surrounding temperature the quicker 

 the movement. When the irritation ceases the leaf 

 will gradually reassume its former position. Fresh 

 irritation produces again a similar phenomenon. 



