ADJUSTMENT TO SURROUNDINGS 



129 



the dark.^ 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- 



Why set in the dark? 

 



