THE STEM AND THE LEAF 



55 



different from that of dicotyledons. Many monocotyledons, 

 such as the rattans, are remarkable for the extraordinary length 



and slenderness of their stems, 

 which often scramble for hun- 

 dreds of feet over the tropical 

 forest. 



52. Arrangement of leaves 

 upon the stem. A glance at any 

 leafy twig usually suffices to 

 show that the leaves do not 

 spring from it haphazard but 

 are definitely arranged. The 

 commonest methods of leaf 

 arrangement are the opposite 

 plan, in which the leaves spring 

 from the nodes in pairs (Figs. 

 39 and 40), as in the maples, the 

 ashes, the mints, and many other plants ; and the alternate plan, 

 in which the leaf origins form a spiral about the stem, as in 



FIG. 39. Top view of vertical shoot 

 of " syringa " (Philadelphus) 



The leaves are arranged in pairs and 

 each pair overlies the spaces between 

 the pair below it. One third natural size 



FIG. 40. Top view of a horizontal shoot from the same shrub shown in Fig. 39 



The leaves spring from the branch in the same order as do those of the vertical 

 branch, but by a twisting of the leafstalks the blades are made to lie nearly in a 

 horizontal position and thus secure abundant illumination. One third natural size 



