148 



LIFE S BEGINNING ON THE EARTH 



thus bends over to the illuminated side because of its greater 

 flexibility on this side. It seems likely that a similar proc- 

 ess causes the bending of real plants toward the light. 



Here is a description of how to observe the bending of 

 artificial structures toward the light. Prepare a 5 per cent 

 solution of a lime salt, calcium chloride, pour it into a square 



Fig. 58. Bending of an Osmotic Structure towards the Negative 

 Pole as an Electrical Current Is Passed through the Solution 



The structure first developed upward. After current was sent through 

 the solution, it hent toward the negative pole. 



glass container, and place crystals of soda in it. Light is 

 allowed to shine on one side of the container. The same 

 experiment is performed in a container which is entirely 

 covered by a tin cap. Delicate tubes of calcium carbonate 

 grow in both containers. In the illuminated container they 

 creep up only on the illuminated side, or grow up a fraction 

 of an inch and then bend toward the light. In the shaded 



