( 31) 



Usually there are three points formiug a triangle, or more and then forming 

 either a curved line (Asimina), a horseshoe-shaped line {Cephalanthns)^ 

 or a closed chain following the outline of the scar {Morns, Sambuciis, Frax- 

 i«M.s), or separating in groups (Ji/_(7Zajis, Carya, Gijmnocladus). The marks 

 are somewhat concave {Acsculus) or convex i^Lindera). 



THE TWIGS. 



The direction of the twig commonly agrees with the direction of the 

 bud. The Sassafras has a peculiar growth : the secondary shoots of the 

 summer from the lower buds attain a greater length than the primary ones, 

 and as the shoots are curved upward, the whole has the appearance of a 

 chandelier {V\. Ill, Fig 1 }. The shoots are either smooth (Fraxinus 

 americana and sambucifoUa, Acer, Crataegus), or pubescent (Fag^is, 

 Bi'tula), or rough hairy {Cori/lm, Chnus fulva), or tomentose-pubescent 

 (^Fraxinus pubcscens, C'ari/a olivae/ormu, Diospyros), or prickly, and then the 

 prickles are placed irregularly on the bark {Rosa, Ruhus, Smilax), or there 

 is only one on each side of the scar, representing a stipule {Rohinia, Zan- 

 thoxylon). Prickles should not be confounded with spines (or thorns'). 

 Ribcs has a spine below the persistent base of the leaf-stalk, and this rep- 

 resents a bract. 



In many species we see ridges running downward from the leaf-scara 

 {Popxdus monilifera, Rhus toxicodendron) , in some species with opposite 

 leaves these ridges are very sharp and prominent, and the twig becomes 

 quadrangular {Fraxinus quadrangulafa , Euonymus atropurpureus). 



The color of the twig is mostly brown, but other colors occur, 

 red {Cornus sericea), purplish (Cornus altcmifolia, Asimina) yellowish 

 {Platanus), green {Sassafras, Euonynms, Staphyl a, Negundo), grayish 

 (Fraxinus sambucifolia, Rhamnus), white, thickly covered with a white 

 woolly pubescence \SaUx Candida). 



THE PITH. 



The pith in a horizontal section of a twig shows different forms in the 

 different species, and in the same individual. In the middle of the meri- 

 thall (space between two single leaves or pairs of leaves or whorls), it is 

 more or less circular in the majority of our species ; but sometimes it shows 

 a hexagonal shape in species with opposite leaves ; in those with five leaves 

 in two circuits, a pentagon {Sassafras, Liquidamhar), or a five-rayed star 

 {Quercus, Popmlus). Near the upper end of the merithall (wrongly called 

 "joint,") the form of the pith is modified by projections towards the leaf 

 or pair of leaves. 



The vertical section in Juglans and Celtis shows the pith in horizontal 

 plates. I have observed this only in one other plant of our flora, the Phy 

 tol-acca.. 



The color of the pith is mostly whitish, pure white in Sassafras, often 

 with a rosy tinge in Tilia (cream color when olderj, yellowish in Rhus glabra 

 and Rhus toxicodendron, reddish in Gymnocladus, Cornus, Rhus aromatica, 

 greenish in Gleditschia, brownish in Juglans cinerea, Carya amara. 



