ROOTS AND THEIR WORK 



85 



Plant mustard or radish seeds in a pocket garden, place it on 

 one edge and allow the seeds to germinate until the root has grown 

 to a length of about half an inch. Then turn it at right angles 

 to the first position and allow it to 

 remain for one day undisturbed. The 

 roots now will be found to have turned 

 in response to the change in posi- 

 tion, that part of the root near the 

 growing point being the most sensitive 

 to the change. This experiment seems 

 to indicate that the roots are influenced 

 to grow downward by the force we 

 call gravity. 1 



The reaction of the plant (or any living 

 thing] to this force is called geotropism. 

 Roots are stimulated by gravity to grow 

 downward; hence they are said to be 

 positively geotropic. 



Experiments to determine Influence 

 of Moisture on a Growing Root. The 

 objection might well be interposed that 

 possibly the roots in the pocket garden grew downward after 

 water. That moisture has an influence on the growing root is 

 easily proved. 



Plant bird seed and the seed of mustard or radish in the under- 

 side of a sponge, which should be kept wet, and may be sus- 

 pended by a string under a bell jar in the schoolroom window. 

 Note whether the roots leave the sponge to grow downward, or 

 if the moisture in the sponge is sufficient to counterbalance the 

 force of gravity. 



Revolve this Figure in the direc- 

 tion of the arrows to see if 

 the roots of the radish respond 

 to gravity. 



1 The Pocket Garden. A very convenient form of pocket germinator may be 

 made in a few minutes in the following manner: Obtain two cleaned four by five 

 negatives (window glass will do) ; place one flat on the table and place on the glass 

 half a dozen pieces of colored blotting paper cut to a size a little less than the glass. 

 Now cut four thin stiips of wood so as to fit on the glass just outside of the paper. 

 Next moisten the blotter, place on it some well-soaked radish or mustard seeds or 

 grains of barley, and cover it with the other glass. The whole box thus made should 

 be bound together with bicycle tape. Seeds will germinate in this box, and with 

 care may live for two weeks or more. 



