60 FOLDING OF LEAVES [CH. 



The manner of folding of the young leaves in the bud, 

 apart from the scales, is also characteristic in some cases ; 

 e.g. in the Blackthorn, Prunus spinosa, the young leaf- 

 blades are rolled up on the vertical axis with the upper 

 surface interior, so that one edge is inside and the other 

 outside (convolute) ; but in the closely allied Cherry and 

 Bird Cherry, P. Cerasus and P. Padus, the leaves are 

 folded on the midrib, so that the two upper half-surfaces 

 oppose one another like the leaves of a book (con- 

 duplicate), characters which can be utilised in diagnosis 

 (cf. Fig. 29). 



The young leaves or leaflets are con duplicate in the 

 following : 



Cherry Bird Cherry Oaks 



Elms Hazel Blackberry 



Rose Vine Ash 



Magnolia Cherry Laurel Lime. 



Moreover, differences are to be met with in further 

 details of the arrangement. For instance, the young 

 leaves are so folded in Magnolia that their margins all 

 point towards the axis of the shoot on which the bud is 

 borne, their midribs being directed away from it and 

 pointing towards the leaf in the axil of which the bud 

 stands (Fig. 36), and the same arrangement holds good 

 for the Elrns, Hazel, Cherry Laurel, and Lime. In the 

 Oaks, and most species of Prunus, however, e.g. Prunus 

 Amygdalus, P. Avium, P. Cerasus, &c., the margins are so 

 directed as to follow the spiral developed by connecting 

 the leaf-insertions. In the Roses the margins of the con- 

 duplicate leaflets are all turned towards the centre of 

 the bud itself; while in the Tulip Tree (Liriodendron) 

 the directions of the margins are reversed in each succeed- 

 ing leaf, alternately pointing towards the axis of the parent 

 shoot and away from it. 



