and Laboratory Methods. 2267 



Methods in Plant Physiology. 

 X. 



XI. GEOTROPISM. 



In selecting material for experimentation in geotropism care should be taken 

 to use only vigorous, healthy plants ; no credence can be given to results obtained 

 from unhealthy or dwarfed plants. When the roots of seedlings are to be used 

 they should be grown in moss or clean pine sawdust. If the sawdust becomes 

 infested with fungi a new supply should be obtained. All potted plants used in 

 this work should be, if possible, grown out of doors, failing of this, the supply 

 may obtained from a greenhouse, but such material is not as reliable. The light 

 must be carefully excluded from all experiments. While preparing the plant for 

 experimentation it is essential that it be kept in the vertical position until ready 



Fig. 11. — Damp Chamber used in Geotropism. 



to apply the desired stimulus. If the results of two or more experiments are to 

 be compared, the temperature at which the experiments are to be performed 

 must be the same in every case. 



1. Region of Curvature in Roots. Select seedlings of any species having a 

 large, straight main root, from '1-b c. m. in length, e. g., the lupine (Lupmus albus) 

 or the pea (Fis/im sativum). Beginning at the apex mark the root into millimeter 

 spaces for a distance of one centimeter with dots of water-proof India ink. 

 Fasten the seedlings with rubber bands and strips of blotting paper to a bar of 

 wood and suspend them in a small damp chamber. Leave a strip of the surface 

 of the jar uncovered by the paper in such a way that observations may be made 

 without disturbing the seedlings. (Fig. 11.) Arrange the seedlings so that the 

 ink marks may be seen through the window in the jar. Fasten the cover and 

 lay the preparation on its side in a plate which contains enough water to keep 



