BUDS AND BRANCHES 107 



Try to realize the great amount of work which is going on 

 as the buds open, and to determine where the material 

 comes from and how it is utilized. If opening buds are used 

 instead of germinating peas in the experiment we have 

 performed previously (p. 44), you will find that they 

 absorb a large amount of oxygen and give off much carbon 

 dioxide. It has been found that during this period of 

 active respiration many of our common trees lose from 

 20 to 45 per cent, of their total dry weight. This helps us 

 to appreciate the fact that respiration is a wasting or 

 breaking-down process. 



Lilac. Quite different from the rosette type are the buds 

 of the Lilac. If we watch them expanding in the spring 

 we shall see that the leaves are not folded and wrinkled, 

 but lie flat and edge to edge. As the shoot grows and the 

 axis elongates, the leaves are seen to be in crossed pairs 

 which have separated by distinct internodes (see Fig. 205). 

 The arrangement of the leaves on the stem, and the relative 

 positions of leaves of different sizes, stand in strong contrast 

 with what we find in a typical rosette. Compare the leaves 

 from below upwards, and notice the transition from small 

 scales below, followed by larger ones, to the mature leaves 

 with longer, grooved stalks and large, heart-shaped (cordate) 

 blades. The bud-scales of the Lilac are thus reduced leaves, 

 of which the lower, smaller ones fall off as the season 

 advances, not when the bud opens, as in many trees. 



Privet. Now compare the Lilac shoot with a shoot of 

 the Privet (Fig. 65). Note the small, brown scales below ; 

 their arrangement and the varying sizes and shapes, not 

 only of the scale-leaves, but of the green foliage-leaves ; 

 also the varying positions of the blades in shoots taken 

 from the side and from the top of the hedge. How are 

 these differences related to the direction in which light 

 falls on the shoot ? What part of the leaf is concerned in 

 bringing the blade into such a position ? The movement 



