2464 



Journal of Applied Microscopy 



Methods in Plant Physiology. 

 XIV. 



HYDROTROPISM. 



The response of plants to the presence of moisture is best demonstrated in 

 the roots of young seedlings. In practice, however, the student usually finds 

 some difficulty in furnishing an equable supply of moisture near enough the root 

 to have its presence felt. 



The illustration (Fig. 19) shows a method of performing this experiment by 

 which good results may be obtained. The wire hoop by which the cone of net- 

 ting is suspended is about 5 cm. less in diameter than a cylindrical battery-jar in 



Fig. I'.i. — Hydrotropic response of roots. 



which it is suspended. When the cone is nearly filled with damp sawdust, plant 

 seeds of radish {Raphanus sativtis) or white mustard {^Sinapis alba) around the 

 outside, a distance from the netting equal to three or four times the diameter of 

 the seeds. While the experiment continues the cone of sawdust should be sup- 

 plied with water once each twenty-four hours ; after watering it, allow the water 

 to drain away before replacing it in the battery-jar. No water should be allowed 

 to stand in the jar nor should a cover be placed on the jar. The preparation 



