CHEMISTBY AND PHTSIOS OF PLANTS. 91 



O) Cover the end (30 to 40 centimetres) of a cucumber-plant, bear- 

 ing young flower-buds, with a tight box so as to exclude all light. 

 Notice that the flowers develop perfectly as to size and color, although 

 in total darkness, while Ihe leaves are small and lacking in normal 

 color. 



(Jc) Cover in like manner a portion of a cucumber-plant bearing 

 very young fruit. Notice that the fruit develops in darkness as well 

 (in size at least) as in the light. 



186. Movements of Plants. — Every living plant is capable 

 of moving. In some cases the movement is so small that 

 it is not visible to the naked eye, while in others it is very 

 evident. It is popularly supposed that animals alone have 

 the power of movement, and that this power is one of the 

 prominent distinctions between plants and animals. In 

 fact, however, no plant is wanting in the power of move- 

 ment, and there are many plants which are much more 

 active than certain animals. 



Only an outline of this interesting subject can be given 

 in this place, and the student who wishes to pursue the 

 subject further should consult Mr. Darwin's book, "The 

 Power of Movement in Plants," published in 1881. 



187. Mr. Darwin has shown by a great number of obser- 

 vations that as soon as a seed germinates every part of the 

 embryo begins moving in various directions. Thus the 

 little root at once begins a sort of revolving motion, its tip 

 describing more or less curved figures. This revolving or 

 bending in succession towards all points of a curved figure 

 so as to describe an ellipse or circle is called circumnuta- 

 tion, an inconveniently long word for what is, as we shall 

 see, a very common thing in plants. 



188. By the circumnutation of a root it is enabled to 

 find those places in the soil which offer the least resistance 

 to its passage. Moreover, it has been shown that the tip 



