1 68 OUTLINES OF PLANT LIFE. 



smaller protoplasmic bodies within the cell, such as the 

 nucleus and the chloroplasts, are capable of moving about. 



II. Movements of multicellular members. 



239. Forces. — The movements of multicellular parts may 

 be brought about either by special organs known as motor 

 organs, or by the unequal growth of the immature parts. 

 Motor organs are generally responsible for the movements of 

 mature parts, while movements of the younger regions are 

 generally due to growth. The force exerted by the motor 

 organs is dependent upon the altered turgor of the cells of 

 which the organ is composed. If the cells upon one side of 

 it lose their turgidity, those upon- the other, being unresisted, 

 will extend and- bend the organ toward the side upon which 

 the turgor was diminished. It will be convenient, therefore^ 

 to distinguish movements due to growth and movements due 

 to variation in turgor. 



240. (A) Movements of growth. — These depend upon 

 some inequality in the rate of growth of the organ concerned. - 

 They are of two sorts, (i) Those in which variation in. 

 growth is produced by causes not yet known (apparently in- 

 ternal) are called spontaneous movements. (2) Those in 

 which the variation in growth results from stimulation by- 

 external agents are called paralonic movements. 



241. I. Spontaneous movements. — Among spontaneous 

 movements are those in which the variation in growth occurs 

 upon different sides of a cylindrical organ, or the two faces 

 of a broad one. The opening of all flower and leaf buds 

 illustrates this movement, which is called nutation. During 

 the development of the interior parts, the outer leaves (often 

 scale-like) which protect them grow more rapidly upon their 

 outer (dorsal) surfaces. They are thus pressed together into- 

 a compact bud. When the internal parts are suitably de- 



