NATURAL SCIENCES OF PHILADELPHIA. 117 



nation became stipular sheaths after having been partially organized as leaf 

 blade ; and that Liriodendron differs from Muynolia only in possessing a greati r 

 power of adnation. 



Notes on SILPHITJM LACINIATUM, L. The Compass Plant. 



BY THOMAS MEEHAN. 



It is at once the strength and the weakness of science that it takes little on 

 trust. One would suppose that, after the positive facts given by President 

 Hill in his paper before the recent meeting of the American Association, there 

 was no room for doubt that the edges of the leaves of Silphium laciniatum had 

 an average bearing north. But I find men excellent, acute observers who 

 doubt the facts. They say " We took the trouble to examine the plants on 

 the spot, and found not the slightest trace of any such tendency; we want no 

 better evidence than that of our own senses." 



As before suggested, it is an excellent habit to verify, for ourselves, the 

 facts reported by others there is far too little of this habit, but when the 

 observations conflict, it is safer to assume that both are right, and that there 

 is something yet undiscovered which would harmonize the opposition, than 

 that either one is wrong. 



In this matter of the Silphium or " compass plant " I was able to find this 

 missing link, and to see that both parties were right. 



When I first saw the Silphium, to any great extent, in its natural localities, 

 there was not the slightest indication of this northern tendency. It was a 

 great surprise, as a limited knowledge of it before had taught the reverse. I 

 determined to watch a plant carefully on my own grounds the next year. The 

 result was just as described by President Hill. There was the unmistakable 

 northern tendency in the leaves when they first came up, and until they were 

 large and heavy, when winds and rains bore them in different directions, and 

 they evidently had not the power of regaining the points lost. This often 

 took place by their own weight alone, especially in luxuriant specimens. .Mr. 

 Hill says it was in June when he saw them on the prairies, all bearing north ; 

 when I saw them, and not doing so, it was early in September, and then no 

 doubt the mechanical causes I have referred to, had been in operation. 



The plant I have had in my garden now for some years affords much in- 

 terest in many respects. I learned an useful lesson from it this year, in refer- 

 ence to the relative rates of growth in the different parts of the inflorescence. 

 Noticing that there appeared to be no growth in the disk florets in the day, 

 I determined to note accurately one morning during the last week in August, 

 exactly when growth did commence. The ray flowers close over the disk 

 during night, and at 4 A. M., with day just dawning in the east, I found the 

 ray petals just commencing to open back. In the disk there are about fifteen 

 coils of florets in the spiral. There appeared no motion until 4.40, although 

 no doubt growth commenced at 4, when the ray petals were in motion, but 

 too slow to be perceptible. At 4.40, however, the five outer circles were evi- 

 dently slightly elevated above the others in the disk. Then follows the fol- 

 lowing record in my diary : 



4.45. The five divisions of the corolla split open. 

 4.50. Corollas grown three thirty-seconds of an inch. 

 4.55. Divisions of corolla fully expanded. 



5. Florets two-eighths above the rest of the disk. It might be well to say 

 here that there was no growth in any this morning but in the five outside 



rows we are speaking of. f Q ti 



5.5, 5.10. No apparent change except that some which were not so perfectly 



opened as the others seemed to become so. ' *, 



5.15. Pistil and mass of stamens slightly elevate above the level of the 



corolla. 



1870.] 



