1 8 82.] On the Compass Plant. 



O20 



of the day; the other was placed so that from sunrise until io 

 o'clock, and from 3 o'clock until sunset, it was exposed to the 

 sunlight, but from 10 to 3 was in the dark. In the first case the 

 leaves did not assume a meridional position, but in the second 

 they did. All this shows that the meridional position is produced 

 by the sun when near the horizon." 



To this can be added that Dr. Engelmann, in a letter to me of 

 28th Feb., 1882, as also in his article in the Gardeners' Chronicle, 

 above mentioned, adds that observations with a microscope show 

 that the number of stomala on the two faces is equal, thus 

 " showing a similar anatomical structure " to that of the Silphium 



The compass plant shows its peculiarity best in mid-summer, 

 when the plant is in full growth prior to the changes which the 

 approach of autumn makes in most plants. It is also best shown 

 in the little hollows on the prairies, where the radical leaves are 

 somewhat sheltered from the winds, and where they will be seen 

 all parallel to each other. There are also great varieties in the 

 size and growth of the 5. laciniaiiun, both in the radical leaf and 

 in the flowering plant. I have myself seen the polarity exhibited 

 in a much more marked manner in some regions than in others. 

 In this respect in Iowa it was never so apparent as on the prairies 

 in Missouri, Arkansas and the Cherokee nation. 



And I was pleased to hear from Dr. Gray that Sir Joseph 

 Hooker saw it in Southwestern Missouri, and in mid-summer. 

 On reaching Boston in 1877, Dr. Gray says, that one. of the 

 first requests of that distinguished botanist was to be shown the 

 compass plant, and Dr. Gray took him to that region. So that 

 in the Botanical Mi^azinc for January, 1 88 1, he says: 



" I have not been able to detect any orientation of the leaves 

 in the Kew cultivated specimens, but these not being planted in 

 a good exposure all round, are out of court as witnesses. On the 

 other hand, when traveling on the prairies with Dr. Gray in 1877, 

 I watched the position of the leaves of many hundred plants from 

 the window of the railroad car, and after some time persuaded 

 myself that the younger, more erect leaves especially, had their 

 faces parallel approximately to the meridian line." 



Dr. Gray in the same article (as quoted by Sir Joseph Hooker) 

 sa ys : " But repeated observations upon the prairies with measure- 

 ments by the compass 1 of directions assumed by hundreds of 



Assoc, (see page 18 of Proceeding), Professor R. Morris said: '-In surveying on 



