( 30 ) 



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 to'ward the leaf-scar ( U7mus, 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 (Car^a alba, PL IV, 

 Fig. 17). 



The blade of the leaf is either conduplicate (^Prunus*, AmelancMer, 

 Asimma, Cercis, Ulmus, Tilia), or plicate (Acer, Hamamelis, Rihes), or 

 involute (Euonymus, Clastrus, Staphylea, Populus, Viburnum'), or re volute 

 {Sal/'x, Ptelea) or convolute (the leaflets of Gary a, PI. IV, Fig. 17), or 

 equitant (Cornus, PI. I, Fig. 24, or open and slightly concave (^Cepha- 

 lanthus. Sassafras^ . 



A very singular arrangement we observe in Lirioilendron, PI. Ill, 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 ( ^i^erczis) ; they are sometimes concay e {Ampelojjsis, Catalpa), 

 or convex ( Uhyins). 



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 (^Oornus, Viburnum), or triangular (Populus), or semi-circular 

 {Praxinus, Quercus), or elliptical (^Liriodendrori), or three-lobed {Cratae- 

 gus, Cercis, Amorpha), with five sharp angles {Lonicera Jiava'), or oval with 

 the upper end truncate or emarginate {Tecoma, Catalpa, Sassafras), or 

 heart-shaped {Rhus toxicodendron, GledifscJiia, Juglans, Caryd), 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 Prunus proper have convolute leaves. 



