1897.] NATURAL SCIENCES OF PHILADELPHIA. 191 



the branches are comparatively weak, but when they have gathered 

 strength the terminal leaflets develop into a stroug tendril. For 

 instance in Bignouia venusta " the leaves are opposite ; lower ones 

 ternate and without tendrils, upjier ones conjugate or pinnate with 

 one pair of leaflets, and furnished with tendrils." The quotation is 

 from the Botanical Magazine, Vol. 46, p. 249, so that those who have 

 not the plant at hand, may see the different forms of leaves in the 

 plate. The one leaf has become a petiole, and is again trifid at the 

 apex — these branchlets again becoming leaflets in other species. 

 Whoever has had the opportunity to study some of the strong grow- 

 ing Bignoniaceae of Central America, must be fully impressed with 

 the woody character of these tendrils. They are as truly ligneous 

 as are those of Vitacese, which are conceded to be of axial origin. 

 When, therefore, we find a plant with a leaf normally trifoliate, 

 transform the terminal leaflet into a permanent woody tendril, it is 

 difficult to understand the necessity for the " abnormal and excep- 

 tional " view of these cases. If we say leaf-blade is the foundation 

 of all cauliue structure, we are not surprised when a leaflet of Big- 

 nonia becomes of the nature of stem, and we are not left to mere 

 position on the axis before we can determine the origin of what is 

 actually the same thing. 



POLARITY IN THE LEAVES OF THE COMPASS AND OTHER PLANTS. 



Those who try to live and learn are often suprised to find some 

 conclusion, which in earlier years we thought unassailable, sud- 

 denly shattered by the logic of facts. In my own case it is not un- 

 usual to note that beliefs which in a limited sphere seemed founded 

 on a rock, were wholly washed out when opposed by a more general 

 application. Of this class is my former faith in the polarity of the 

 root-leaves of the Compass Plant, Silphium laciniatum. 



It is just as true to-day as it ever was that the root-leaves stand 

 erect instead of curving more or less toward the horizon as the root 

 leaves of most herbaceous plants do, and that the edges of these 

 leaves are in a more or less north and south line. The faces of the 

 leaves are of much the same construction, and are presented to the 

 east and west respectively. It seems very reasonable to suppose 

 that the leaves are polar because of the similarity in the structure 

 of what would usually be the upper and lower surfaces ; that be- 

 cause both surfaces are struggling to get to the full light, and 

 having equal power neither can win, and hence the edges must 



