buds the pairs stand at right angles, the lower ones outside, those higher on 
the shoot inside (PI. I, Figs. 21-25'. In the bifarious species the leaves 
are located side by side, the lowest outside, the highest in the middle, the 
posterior side of the midrib looking toward the leaf-scar ( Ulmus , PI. IV, 
Fig 14) ; or they stand opposite, the lower inclosing the upper ones ( Celtis , 
Plate IV, Fig. 15), the posterior side of the midrib looking toward the 
bud-scales. In those with the spiral position of the buds the leaves are 
arranged in the same way ; the posterior side of the midrib looks toward 
the corresponding scale ( Populus , PI IV, Fig. 16). When the species has 
compound leaves, the leaflets lie either side by side or in a half-circle, the 
uppermost in the middle, the lower ones at the sides ( Carya alba , PI. IV, 
Fig. 17). 
The blade of the leaf is either conduplicate (Primus*, Amelanchier, 
Asimina , Cercis, Ulmus , Tilia ), or plicate (Acer, Hamamelis, Ribes ), or 
involute ( Euonymus , Ctlastrus, Staphylea, Populus, Viburnum ), or revolute 
(Salix, Ptelea ) or convolute (the leaflets of Carya, PI. IV, Fig. 17), or 
equitant ( Cornus , PL I, Fig. 24, or open and slightly concave ( Cepha - 
lanthus , Sassafras). 
A very singular arrangement we observe in Liriodendron , PL III, Fig. 
4. The leaf is conduplicate and bent inward from the upper part of the 
petiole, and the cover of the bud is nothing else than the two stipules of an 
abortive leaf. 
LEAF-SCARS. 
At the base of the bud we observe the scar of the fallen leaf, an area 
of varying form, covered with a thin layer of corky matter which is formed 
in the latter part of the season and separates the leaf from the shoot ; and 
within this area we notice the vestiges of the vascular bundles that enter the 
leaf- stalks. 
The scars are either flat upon the stem ( Aesculus ), or on a projection, 
pulvinated (Quercus); they are sometimes concave (Ampelopsis, Catalpa), 
or convex ( Ulmus). 
The form of the scar depends on the form of the base of the leaf-stalk, 
and is very variable. It is narrow, nearly linear ( Negundo ), or crescent- 
shaped ( Cornus , Viburnum), or triangular (Populus), or semi-circular 
(Fraxinus, Quercus), or elliptical ( Liriodendron ), or three-lobed (Cratae- 
gus, Cercis, Amorpha), with five sharp angles (Lonicera flava), or oval with 
the upper end truncate or emarginate (Tecoma, Catalpa, Sassafras), or 
heart-shaped (Rhus toxicodendron, Gleditschia, Juglans , Carya), or horse- 
shoe shaped (Rhus glabra , Ptelea), or ring-shaped around the bud ( Plata - 
nus, Dirca). Here the bud was covered by the hood shaped basis of the 
leaf-stalk. In Dirca, the bud is situated in a cup-like cavity the margin of 
which forms the leaf scar. When two scars of opposite leaves meet (Ne- 
gundo'), the twig seems to be articulated. 
The marks of the vascular bundles are very characteristic, presenting 
sometimes one point in the center (Celtis), or a horizontal streak (Sassafras). 
*The European species of Primus proper have convolute leaves. 
