16 INTRODUCTION. 



acuminate at the tip : but some leaflets are strongly cordate 

 below, and some are abruptly cuspidate. The form, although 

 speaking generally it may be called obovate, is sometimes 

 so much and regularly narrowed below as to become almost 

 wedgeshaped, or it may narrow so slightly as to be very 

 nearly oval, or, in a few cases, the sides are so parallel and 

 the two ends so truncate that the leaflet is almost square, 

 with a central terminal cusp. Many intermediate forms are 

 found to which attention should be paid. In some leaves 

 the lower pair of leaflets partially overlaps the intermediate 

 and, rarely, the latter overlap the terminal leaflet; or, the 

 lower leaflets are directed backwards, toward the petiole, 

 so as to leave a clear space between them and their neigh- 

 l)ours. Those differences in the direction of the leaflets are 

 usually constant and therefore deseiwing of attention; but 

 in some species they are not wholly to be depended upon. 

 It is often very difficult to determine what has been the 

 direction of the leaflets after the specimen has been pressed 

 in preparation for the herbarium. The whole leaf is convex, 

 flat, or concave above, and the edges of the leaflets are either 

 similarly curved or flat; or, the whole leaf may be flat and 

 the edges of the leaflets may curve upwards or downwards 

 so as to be concave or convex. The edges of the concave 

 leaflet are usually wavy. The leaflets are sometimes simply 

 and finely dentate or serrate or doubly so; or the double 

 teeth are so large, especially in the upper half of the leaflet, 

 as to resemble dentate or serrate lobes. These lobes are 

 either directed towards the end of the leaf or their tops turn 

 more or less from it : this seems to be a difference of some 

 value, for there are cases in which individuals belonging to 

 species which usually have well-marked lobed dentition have 

 the lobes reduced to very broad but low double teeth, and 



