ADJUSTMENT TO SURROUNDINGS 
I2Q 
the dark. 1 The air in the dish may be kept moist by a 
strip of damp filter-paper placed around the circumference 
of the dish, inside. 
FIG. 86. Experiment to demonstrate positive geotropism in the root 
of a seedling of lupine (Lupinus albus). S, metal stand; P, Petri dish, 
with edges lined with moist filter-paper. The seedling is pinned to a strip 
of sheet cork. The four views are of the same seedling at the successive 
hours as indicated. (Apparatus after W. T. Bovie.) 
At the end of 12 hours, more or less, the sprout, on ac- 
count of its positive geotropism, will have responded to 
the pull of gravity by curving downward, until the por- 
1 Why set in the dark? 
9 
