1 882.] On the Compass Plant. 627 



radical leaf, but the flowering plant. The reader of those jour- 

 nals will look in vain at the drawings to comprehend the polarity 

 of the plant. 



The experiments to which I refer were made on the radical 

 leaves, which grow to the height of from one to two feet, and are 

 strong and robust, and not easily disturbed by winds or other 

 extraneous objects, and therefore the more useful as a guide on 



These experiments have been made since my paper was read 

 in 1849 to the American Association. By them I became satis- 

 fied that Dr. Gray was right, in 1849, in attributing the pecu- 

 liarity to the action of light. 



1st. — I applied a very delicate galvanometer to the points of 

 the leaves, so delicate that it should have detected the minutest 

 quantity of magnetic or galvanic action, and no deflection was 

 apparent. 



2d.— Powerful magnets did not appear to deflect the leaves. 



3°". — The plant was grown in a box, and after the leaves pre- 

 sented their edges north- and south, the box was turned ninety 

 degrees, and in a few days the leaves were seen to struggle to 

 get back to their former meridional position. 



4th.— Neither J. W. Bailey, LL.D., professor of chemistry at 

 West Point, nor Professor John Torrey, at Princeton, after careful 

 analysis in 1842, could detect any traces of the magnetic oxide 

 of iron in the plant, or iron in any shape. 



Mr. Edward Burgess, by request of Professor Asa Gray at 

 Cambridge, about 1870, examined with a microscope the two sur- 

 faces of the leaf of the 5. laciniatinn, and found the structure of 

 the epidermal tissue of the two surfaces to be similar, and also 

 the number of stomata in each face to be about equal. Leaves 

 generally turn toward the light, and the under surface in such 

 cases is more " copiously furnished with stomata, or breathing 

 Pores as they are often inaccurately termed, which serve to pro- 

 mote a diffusion of gases between the external air and the inter- 

 cellular cavities within the tissue, and especially an abundant 

 exhalation of aqueous vapor" (VV. F. Whitney in American 

 Naturalist for March, 1871). 



My theory is this: all leaves will turn their upper faces toward 

 the light. But in the compass plant (I speak now of the radical 

 leaf ) tr »e stem comes up vertically and stiffly from the root. 



