1 86 THE TEACHING BOTANIST 



In geotropis'ii there are many additional experiments very 

 easy to try, and very instructive. For example, while the side 

 roots are growing, the germination box may be tipped up 

 through 45 in a vertical plane, when a beautiful response to 

 the changed direction takes place ; to show that the upward 

 growth of stem is geotropic, a small plant may be placed on 

 its side in darkness for a day ; also plant a Bean in a small 

 pot of Sphagnum moss, and after it is well up, turn pot 

 and all upside down, and support it in that position for 

 two or three days, after which the moss is to be removed. 

 A most valuable experiment, proving that growth is concerned 

 in bringing roots into the vertical position, is as follows : 

 Place a soaked Horse Bean in moist Sphagnum moss, with 

 its hypocotyl pointing downward ; after the root has grown 

 one inch long, remove it, and, keeping it from drying in the 

 process, mark rings a millimetre apart upon it, from end to 

 end, with waterproof India ink. This may best be done by a 

 thread moistened with the ink and kept stretched on a spring 

 made of wire. Replace the seed in the moss with the root 

 horizontal, and, after it has again turned downward, note the 

 position of the rings. 



If students are not satisfied that gravitation is the guide to 

 direction in ordinary plants, but think that it may be moisture 

 which guides the roots into the soil, or light which guides the 

 stems upward, etc., very simple experiments may be invented 

 to prove that these influences do not thus act. Thus, light 

 may be thrown upward upon a plant, turned upside down, 

 by means of a mirror, the plant being covered with a dark 

 box above. Again, seeds may be placed in the centre of 

 a large box of Sphagnum, and watered from above ; and other 

 experiments equally simple may be devised by the teacher to 

 meet each point. 



