BUDS AND BRANCHES 117 



clothed with silky hairs. As they emerge you will see that 

 the leaves hang downwards in such a way as to expose 

 only their upper surfaces (Fig. 76), thus reducing loss of 

 water by transpiration and loss of heat by radiation, as 

 in the Horse-Chestnut. Finally, they are raised by increased 

 growth on the under surface and thus the blades are brought 

 into a horizontal position. 



On comparing a given shoot with that of the Lilac we 

 find similarly that the lowest and oldest leaf is the smallest, 

 the highest and youngest leaf the largest (see Fig. 191, 2). 

 This difference in size, however, together with the horizontal 

 position of the blades, results in the leaves not only forming 

 a flat plate, but the available space is occupied with the 

 least amount of overshadowing. In this way a leaf- 

 mosaic is formed, but by a very different means from that 

 of the Sycamore or Horse-Chestnut. 



These features should be looked for in other trees, such 

 as Elm (see Fig. 197), Hornbeam, and Hazel, and also in 

 herbaceous plants. Leaf-mosaics are common in the plants 

 of temperate climates. 



Examine a winter twig of the Beech similar to that 

 shown in Fig. 74. Note that there is a slender zigzag 

 shoot at the tip with a bud at each bend. Below that, 

 a series of scale-scars (s.s) shows the limit of the year's 

 growth. These features are repeated as we pass backwards, 

 six such portions being shown in the figure at 1-6. At the 

 bends, in place of buds, are short branches with many 

 scale-scars and terminated by a bud. Clearly these 

 branches grow very slowly and the leaves produced by 

 such buds are separated by very short internodes. Such 

 short, slowly- growing branches are called Spurs, or Dwarf - 

 shoots. Figs. 74, 75, 76 show what is produced from such 

 a shoot in the following spring. The end bud has grown 

 into a long, slender, slightly zigzag shoot with leaves at 

 the bends. The next two lateral buds form the beginnings 



