632 On the Compass Plant. [August, 



also clearly apparent. Dr. J. G. Hunt, of Philadelphia, a distin- 

 guished microscopist, examined some of the leaves of the Thuja 

 oricntalis which I sent him, and says, June 19, 1881, that "there 

 is no structural difference in the two sides of the leaves on the 

 plant." It is only in the young plant three or four feet high that 

 this is seen, for in the beautiful clumps of the Thuja oricntalis 

 eight to twelve feet high, the leaves, all vertical, radiate in every 

 direction from the trunk of the tree. 



A friend from Louisiana, the late Professor C. G. Forshey, 

 wrote me that he had formed the same conclusion concerning 

 this plant as to its meridional position under certain circum- 



Mr. William Saunders, superintendent of the garden at the 

 Agricultural Department in this city, informs me that the leaves 

 of the Eucalyptus poly anthemus are vertical and have the number 

 of stomata the same on both faces. But confined in a conserva- 

 tory nothing is known of any tendency of the leaves to face the 

 rising and setting sun. 



If it is asked why I was at an early date disposed to look to 

 other agencies than light as possibly concerned in causing the 

 peculiarity of the compass plant, I answer that I was fresh from 

 the study of electro-magnetism. Read section 105 of Roget's 

 Electro-magnetism on the electrical spiral coil (the "Solenoid"), 

 by which currents of electricity cause it to act when suspended 

 on a vertical axis, like the magnet in pointing to the north. Read 

 the treatises on vegetable physiology which speak of the spiral 

 coils in the leaves of various plants, and " that one of the most 

 remarkable properties of vegetable membrane is its power of 

 allowing fluids to pass slowly through it, even though no visible 

 pores or apertures can be detected in it."' " The spiral filaments 

 are found in leaf-stalks from which their spiral fibers can be un- 

 coiled." Thus it experiment and dissection of the compass 

 plant could in any way favor the idea of such anatomical struc- 

 ture, its polarity might be sought for in electric currents, 

 this day the best received theory of the magnetism of the eart 1 

 is Ampere's, that it is due to electric currents from west t 



und the crust of the globe ; and that a steel magnet 1 



caused 



electric currents transverse to its axis and perm 

 itire length. 

 But when one agency is sufficient to account for the phenome- 



