78 APPENDIX I. 
EXPERIMENT 23. TO SHOW THE EFFECT OF WATER. 
Grow various seeds on a suspended moistened sponge; under 
the influence of gravity roots usually grow downward. Why 
do many of the roots, as shown in the experiment, grow to- 
ward and into the moist sponge, in opposition to gravity (hydro- 
tropism) ? 
EXPERIMENT 24. TO SHOW THE EFFECT OF 
TEMPERATURE. 
(a) On germinating seeds. 
Sow seeds in the same favorable conditions for growth except 
in temperature; some in a place of low, others in an ordinary, 
and still others in a place of high temperature. After several 
days observe and explain the results. 
(6) Place young growing leafy plants in the same conditions 
as in (a), and in like manner observe and explain the results. 
