94 IIXIM'JIIMENTAL PLANT I'HYSIOLOCiY 



from the light, the angle of inclination boing greater 

 for the shoot than for tlic root. The HcocllingH gnwing 

 in white light are most affected (Fig. 4:"), A). For thoHo 

 growing in blue light the directiyo influence is rather 

 less (ifg. 45, }'.). Tho seedlings upon which the red 

 light falls are only slightly inclined from tho vertical 

 (%, 45, c). 



uiferences.— The blue rays have the greatest influerice 

 in (lotermiriing the direction taken by the different 

 parts of tho plaiilH ; very httle influence is exerted by 

 the red rays. 



Experiment 60 



Aim. — To find out whether moisture affects the 

 direction of growth of the root. 



Method.— Two small sieves or gravy strainers arc 

 suitable for tbi.s experiment. These must be filled with 



Fro, 'I'i 



damp sawdust and planted with mustard seeds. 'Jlic 

 meshes must be large enough for the roots to pass 

 through. The sieves are placed over two ttimblers or 

 beakers, one of which contains water, while the other is 

 left empty. The sawdust must bo kept damp. 



Observations.— The roots of the growing seedlings 

 come through the holes of the sieves and l^cgin to grow 

 downwards. 



In the case of the seedlings growing over water the 

 downward growth of tho roots is maintained. In the 

 other case, however, the root-tips soon turn upwards 

 and creep along the damp surface of the sieve (Fig. 46). 



