104 



BOTANY 



give rise to lateral branches, had a very definite arrangement in pairs at the 

 nodes. Such are the maple or horse-chestnut. If, on the other hand, 

 the leaf traces are placed alternate to each other, we can picture a tree with 

 much less regularity in the position of leaves and lateral branches, as in the 



apple, beech, and elm. 



The very tiny scars, which look like little cracks 

 in the bark, are very important organs, especially 

 during the winter season, for they are the breathing 

 lioles of the tree. A tree is alive in winter, although 

 it is much more active in the warm weather. Oxi- 

 dation takes place much more rapidly in the summer 

 because the plant is growing rapidly, and more fuel 

 is consumed to release the energy needed for growth. 

 We shall see later that the leaves are the chief 

 Ijreathing organs of the plant. But all the year 

 round oxygen is taken in by means of the lenticels, 

 as the breathing holes in the trunk and branches of 

 a tree are called. Notice whether the distribution 

 of the lenticels is regular over the surface of the 

 branch. Notice also, that some of the lenticels have 

 become split in the growth of the tree so as to appear 

 as long cracks. 



In the twig of the horse-chestnut another scar 

 will be found at a point between two branches. 

 This scar marks the place where a cluster of 

 flowers was attached. It is called a flower scar. 



Make a careful drawing of the branch, showing, 

 if possible, all the parts we have discussed. Make 

 careful labels for all the parts. 



Adaptations in the Bud of Horse-chestnuTo 

 — If we now turn our attention to the horse-chestnut 

 buds which have been previously placed in water to 

 open, we shall be able to get some notion of the 

 wonderful adaptations of the bud, which fit it for 

 its work. 

 In the first place, a horse-chestnut bud is covered with a sticky material. 

 Not only does this covering keep out unwelcome visitors which might bore 

 into the bud and destroy the tender parts within, but it also serves as a 

 waterproof covering against the icy rains of the late fall and early spring. 

 In the buds which have not begun to open, notice the overlapping position 

 of the scales, like the shingles on a roof. Of what use might this be? In 

 buds which have begun to open, notice that not only have the tiny green 

 leaves been protected by the outer scales, but they have been additionally 

 WTapped in soft, cottony substance. You can easily see that the leaves 

 have been folded together so that the flat surface has had a minimum of 

 exposure. The young leaves are always folded or rolled up in the bud. 

 Two purposes are thus served, protection from frost and from drying by 

 little exposure of the delicate surface, and economy of space by means of 

 the tight and compact stowing away of the parts thus folded. This ar- 



Twig, showing knot (K) 

 and lenticel (L). 



