ABSORPTION AND OSMOSIS 



63 



pointing root, will soon turn downward at the tip, as will all of its 

 branches. This can be repeated with any kind of seeds. It would 

 not do to infer a general rule from one or two cases. 



If a germinating box with well-grown seedlings be turned on 

 its side, the roots will turn down, no matter how often the experi- 

 ment be changed, thus proving the same thing in another way. 

 Our experience with 

 planting seeds in the 

 garden also is a good 

 experiment in the same 

 line; the root turns 

 down, no matter how 

 the seed is placed. 



The same experi- 

 ments prove that stems 

 turn away from gravi- 

 tation's pull. This is 

 called negative geotro- 

 pism, and applies to 

 most plant parts except 

 roots. It is evident 

 that what we call 

 " weight " has nothing <* 



to do with the direction 5 s EB os IN 

 of either root or stem. <* 



,. XX ^>X WET 



-=ST 



nojs 



ROOT 



I 

 i 



Cr 



BY 



INCLINED SIEVE 



If INFLUENCED 

 ONLY 



FIG. 11. Note different direction taken 

 roots, when attracted by moisture. 



by 



The root, though not 

 so heavy as the soil, 

 penetrates it on its way 

 downward, and the 



stem, despite its weight, turns upward, due to this effect of gravita- 

 tion on all the living cells. 



It might be thought that light had something to do with this 

 change of direction in plant parts. How could it be decided by 

 experiment? 



To Prove that Roots Turn toward Moisture. If seeds be planted 

 on the bottom of a coarse sieve which is then filled with wet moss 



