LEAVES AND BUDS. 141 



175. Folding (Vernation) of Young" Leaves. To ensure the 

 close packing of the leaves in the bud each one is usually rolled up 

 longitudinally (more rarely rolled up transversely) ; but sometimes the 

 leaves are nearly flat, e.g. Privet, Holly, Ivy, Willows. Dealing only 

 with longitudinal folding, the leaf may be simply doubled on itself 

 along the midrib (Fig. 48, conduplicate), or it may "be pleated so as to 

 resemble a fan (plicate), or the edges of the leaf may be rolled inwards 

 (involute) or outwards (revolute), or the leaf may be rolled up from one 

 side, so that one leaf -margin is within the coil and the other outside 

 (convolute). The young leaves are conduplicate in Cherry, Rose, Elm, 

 Hazel, Oak, Lime, Ash ; plicate in Maple, Sycamore, Birch, Beech, 

 Hornbeam ; involute in Poplar, Apple, Pear (also in Violet) ; revolute 

 in Plane and Rhododendron (also in Docks) ; convolute in Plum. 



176. The Opening of the Bud. In spring or early 

 summer the winter-bud resumes its development. The young 

 shoot grows and lengthens, pushing aside the bud-scales, which 

 then fall off. Since each scale leaves a scar on the lower part 

 of the bud-axis and this part remains short, a series of closely- 

 set scars is left on the stem. A series of bud-scale-scars 

 ("girdle-scars") is of course seen at the base of each branch, 

 and by examining a twig and noting these series of scars we 

 can easily tell how much the twig has grown each year, often 

 for many years back ; later on these marks are obliterated by 

 the formation of bark, but in smooth-barked trees (e.g. Beech) 

 one can trace the growth back for twenty years or even more 

 by these girdles of scars. 



As the bud-axis elongates, the leaves grow in size and 

 spread themselves out (the leaf -stalks of course helping in 

 this, if present), becoming spaced out on the young shoot. 

 Buds then appear in the axils of the leaves, and these may 

 either develop at once or remain dormant, some of them of 

 course becoming the resting-buds for next year's growth. 



It is easily understood why all of the axillary buds do not usually 

 develop into branches, for if they did the foliage would be too closely 

 packed together, and sufficient light and air could not reach all of the 

 branches and leaves. As we shall see later, trees differ very much in their 

 mode of branching and in the arrangement of their leaves ; thus in the 

 Horse Chestnut and the Beech the outer leaves are densely packed 

 together, so that buds within the crown of foliage have but little 

 chance of developing into leafy branches, owing to the small amount of 

 light which reaches them. In the Birch and Larch, however, the 

 foliage is more open, and the buds nearer to the stem have perhaps as 

 good a chance of developing as the buds at the tips of the branches. 



