APPENDIX I. 77 
Cover the seed with moist cotton and insert the tube in a 
moist chamber. In a few days root hairs in abundance will 
be seen. By ink marks on the tube at regular short intervals 
the region of growth may be determined. 
(6) On stems. 
By ink marks placed at regular intervals on a young grow- 
ing stem the region and amount of growth may be found. In 
grasses the upper portion of each internode must be similarly 
marked to obtain results. Explain. 
Iv. IRRITABILITY. 
EXPERIMENT 21. TO SHOW THE EFFECT OF GRAVITY. 
Using the material as arranged in the latter part of (a) in 
Experiment 1, arrange the plates vertically so that the roots 
and stems lie in a horizontal position, and after some time 
observe the direction of growth of the roots and shoots. 
Which manifest positive and which negative geotropism ? 
To vary the experiment the plant may be entirely inverted. 
EXPERIMENT 22. TO SHOW THE EFFECT OF LIGHT. 
(a) On seed germination. 
Place some seeds with the same favorable conditions for 
growth except that some are placed in the light and others in 
the dark. After several days observe and explain the results. 
(6) Place ordinary young foliage plants in the light and 
others in the dark. After several days observe and explain 
the lighter color of those growing in the dark (etiolation). 
(c) Place ordinary young foliage plants in a position to 
receive light from but one direction. After some time observe 
the change of direction and position of the stem and leaves 
(heliotropism). Reverse the plant and again observe in the 
same way. 
