MOVEMENTS OF PLANTS. 199 



These facts indicate the correctness of the view that the 

 movements are the results of the motility of the protoplasm. 

 261. Movements of Nutation. In the organs of many 

 plants an inequality of growth is often noticeable, one side 

 growing for a time more rapidly than the other. If this is 

 followed by a more rapid growth upon the other side, and this 

 again by a more rapid growth upon the fir^t side, and so on, 

 alternating from side to side, simple movements of nutation 

 will take place, the apex of the organ swaying or oscillating 

 from side to side in one plane. If the tracts of unequal 

 growth pass slowly and regularly around the organ, its apex 

 will describe a circle in its nutation. 



Of simple nutation in one plane many leaves afford good 

 examples ; thus in the bud the growth is greatest upon the 

 outer or under side of each leaf, which, as a consequence, is 

 bent upward, but in the opening of the bud the greater growth 

 takes place upon the upper side. The greater growth of the 

 upper side of an organ has been termed epinasty ; that of the 

 lower side, hyponasty. Many floral leaves exhibit first 

 hyponasty and afterward epinasty, the first in the bud and 

 the second in authesis (i.e., the opening of the flower). 

 Many stamens and styles exhibit nutations of this nature ; 

 thus in Claytonia both sets of organs are at first erect, but 

 afterward they become divergent by epinasty. 



In many cases, particularly in leaves and the parts of 

 flowers, these movements of nutation are controlled by vari- 

 ous external agents, among which light and heat are the 

 most important. To these are to be referred the successive 

 opening and closing of many flowers, and the diurnal and 

 nocturnal positions of the leaves of many plants. 



262. Of the second class of nutations, the leaves of the 

 onion, and the ends of the stems and the tendrils of climb- 

 ing plants, furnish good examples. These rotate through 

 circles or spirals, in the case of the hop and honeysuckle to 

 the left, and in the bean and morning-glory to the right.* 



* To the right, or from left to right, is opposite to the direction of 

 the hands of a watch ; to the left, or from right to left, is in the direc- 

 tion of the hands of a watch. 



