88 EXPERIMENTS WITH PLANTS 



any changes in the color, shape or position of leaves 

 and other parts. What do you think these indicate 1 

 Allow some uninjured plants to go un watered for a 

 time ; do they show the same symptoms I What does 

 this indicate as to the work of the root ? 



In what direction should the main root grow, to do 

 its work most effectively? Does the main root always 

 grow straight down ? Pin soaked seeds on corks in 

 various positions (see Fig. 73), and allow the corks 

 to float on water; pin the seeds in such a position that 

 they will remain partly submerged; cover the dish 

 with a piece of glass. Put some soaked seeds in 

 various positions on the surface of moist soil and 

 cover with an inverted tumbler, or place them in a pot 

 half full of soil and lay a piece of glass on the top, 



to keep the air moist. 

 If the roots bend 

 downward, change 

 the position of the 

 seeds so that they 

 point upward or lie 

 horizontally. Do they 



73. Seeds pinned to corks which are floating begin to gl'OW dOWU- 



onwater - ward again? 



Why does the main root persist in doing this, no 



matter in what position it is placed? The idea has 



been advanced that the tip of the root, being not very 



rigid, droops downward of its own weight and that 



