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TEXTBOOK OF BOTANY 



and some small. These branch veins in turn branch, 

 their branches branch and so on, thus forming a network of 

 veins like that in the cucumber leaf. The leaves as well 

 as the stems and branches of many varieties of beans bear 

 fine, short hairs. If we examine the leaves of a bean plant 

 in the evening or at night, we shall see that their position 

 is somewhat different from what it was during the day. 

 Each leaflet has drooped so as to bring the three leaflets 

 closer together, and the leaf as a whole stands more nearly 



vertical and closer 

 to the stem or 

 branch. These 

 changes in posi- 

 tion are caused by 

 a bending of the 

 leaf-stalk and of 

 the stalk of each 

 separate leaflet. 

 The bending of 

 the leaf -stalk takes 

 place in a short, 

 thickened region 

 near its base. The 

 stalks of the leaf- 

 lets are so short that practically the whole of each stalk 

 takes part in the bending and so corresponds to the thicker 

 part of the leaf -stalk. In the morning the leaves and leaflets 

 move back to the position in which we are accustomed to 

 see them during the day. The changes in the position of 

 the leaves at night are often called sleep movements, although 

 they really have nothing to do with anything like a sleep of 

 the plant. 



164. Roots. The root system of the bean consists of 

 a rather short primary root with many slender branches 

 which themselves branch ; some of the branch roots may 



FIG. 84. A bean leaf in its night position. 

 After Sachs. 



