1 882.] , On the Compass Plant. 63 r 



lobes of the basal half pointed say east and west, Those of the 

 apical half pointed north and south." 

 , My explanation of the east and west position observed by Mr. 

 Fendler is, that while under the action of light the situation of 

 the leaf for a position of stable equilibrium, is to face the rising 

 and setting sun, it might, under the glare of the mid-day sun 

 have temporarily, as a position of unstable equilibrium, taken a 

 posture east and west. This would be when the whole leaf faces 

 toward the south. But the anomaly of " an abrupt torsion of 

 90 in the middle of the blade" (again referred to by Dr. Gray in 

 reference to Professor Farlow's note on Stahl), is one for future 

 observers to scan, who live near the plant on the prairies. If the 

 basal half was not from any cause free to change its direction, the 

 phenomenon would appear to be explained. 



Now as to other plants, reports, after my first communication 

 to the National Institute in 1842, were received from the West 

 by that society, stating that other plants on the prairies were 

 found to possess the same peculiarity. My paper of August, 

 1849, said: " Proper observation and experiments may discover 

 traces of some general law for these results." We have men- 

 tioned above the experiment on the Lactuca scariola. All tends 

 to confirm the idea that the polarity is due to the action of light. 



Besides that plant, Stahl names Aplopappns rubiginosus, Lac- 

 tuca saligna, and Chrondrclla jitncca, and he " believes that many 

 other examples will be found, especially among the plants of dry 

 and exposed regions." 



I have now to add that observations made during the last 

 twelve months on the Chinese arbor-vita?, or Thuja orientate, in 

 this city (Washington), convince me that when raised in a hedge 

 only three or four years old and three or four feet high, its 

 broad leaves will face the rising and setting sun. In the court- 

 yard of Professor C. V. Riley, corner of 13th and R streets, N. 

 W., there are two such hedges of the plants ; one running east 

 and west, the other north and south. Both exhibited the prop- 

 erty. In reference to the former hedge running east and west, if 

 »t might be supposed that the pointing north of the leaves well in 

 view, might be due to the other leaves, except at the ends, being 

 h 'dden from view, interlocked by the closeness of the hedge, I 

 answer : look at the other hedge running north and south, and 

 th e verity of the meridional' position of the leaves is there 



