98 



EXPERIMENTS WITH PLANTS 



glass 1 the direction which seems to you most advan- 

 tageous for the main roots and side roots arid the 



rootlets which 

 spring from the 

 latter ; begin the 

 marking directly 

 over one (or more) 

 of the roots. Ex- 

 clude light com- 

 pletely by covering 

 the glass with card- 

 board or cloth. 



What direction do 

 the side roots have 

 when they burst 

 out of the main 

 root? Do they after- 

 ward change this 

 direction? If so, 

 when? Do you 

 think they solve the problem of direction in the best 

 way? 



Are they guided in the direction they take by light, 

 heat, moisture, food or gravity ? Light has been care- 

 fully excluded. If it were heat, moisture or food that 

 guided them, we should expect to find adjacent side 



1 A mixture of glue and whiting put on with a brush is excellent for mark- 

 ing ; white paint will do, but dries more slowly; yellow pencils for marking 

 glass are good. 



81. 



Apparatus designed to test the behavior of side 

 roots under the influence of gravity. 



