THE COMPASS-PLANT. 105 



chemical analysis disproved this proposition. 

 It was next supposed that the resinous char- 

 acter of the leaves render them susceptible 

 to electrical currents, but rosin being a non- 

 conductor of electricity, this hypothesis also 

 fell. Dr. Asa Gray suggested the true expla- 

 nation of the phenomenon : both surfaces of 

 the leaf have essentially the same structure, 

 there being nearly as many stomata on the 

 upper as on the under surface, — about 

 52,700 to the square inch above, and 

 57,300 below ; this renders both surfaces 

 equally sensitive to light, and the leaf twists 

 upon its petiole until both sides share equally 

 in the sunlight. 



The compass-plant occurs in open glades 

 and on prairies from Michigan to some three 

 hundred miles west of the Mississippi. It 

 is a large and coarse herb, attaining the 

 height of six or seven feet. It is one of 

 the Compositae. This is the plant of which 

 Longfellow speaks in Evangeline, mistaking 

 it for a delicate species : — 



" Look at this delicate plant that lifts its head from the mead- 

 ow; 

 See how its leaves all point to the North as true as the 



magnet : 

 It is the compass-plant that the finger of God has suspended 

 Here on its fragile stalk to direct the traveler's journey 

 Over the sea-like, pathless, limitless waste of the desert." 



