44 LIVING PLANTS 



its coarse, rigid stem, and wrote, "Look at 

 this delicate flower * * * that the finger of 

 God has suspended here on its fragile stalk,^^ 

 but in later editions of the poem changed the 

 wording as above. 



The compass plant of the prairies and the 

 compass plant of the highways differ, in that 

 the former exhibits polarit3^ chiefly in the rad- 

 ical leaves (large, coarse leaves, a foot or two 

 long), and the latter in the stem leaves. 

 Otherwise the phenomenon in the two plants 

 is practically identical. 



There was much conjecture for a long time 

 as to the cause of this unique behavior. It 

 Explanation ^^s suggested that the magnetic currents of 

 ? *x^ J^^"~ ^^^ earth acted upon iron oxide in the leaves, 

 or that the abundant resin in the plant 

 brought about electrical disturbances. But 

 both theories failed when put to the test, and 

 others stood no better until the relation to 

 light was observed. It was found that plants 

 grown in boxes, if turned one quarter round, 

 readjusted their leaves to again point north 

 and south. This occurred when the plants 

 were grown in bright light, but not when 

 grown in darkness. It was also found that 

 the number of stomata (breathingpores) was 

 essentially the same on both surfaces of the 

 leaf, while ordinarily there are very many 

 more below than above. Further uniformity 



iar trait 



