THE STUDY OF TUBES. 



255 



lenticels, and their use is to permit of the passage of gases 

 to the interior of the twig. When the activities of the 

 plant are almost at a standstill in winter, these lenticels 

 are closed by the growth of ordinary cork tissue across 

 them (Fig. 128). 



On the terminal section of the twig are a number of 

 buds ; they occur in pairs, and each pair is placed at right 

 angles to the pair below. There is also a bud at the tip of 

 the branch. All the buds are enclosed in brownish red 

 or reddish green scales. All this is easily verified. 



Beneath each of the paired buds a pale somewhat cres- 

 ceiitic scar is visible. On this pale scar a row of darker 

 coloured dots occurs. 

 Can we tell what these 

 scars are ? They 

 mark the place where 

 this year's leaves were 

 attached ; their pale 

 surface is due to the 

 layer of cork which 

 cuts off the leaf in 

 autumn, and the small 



, , -i Fig. 130. Portion of Sycamore twig : a, pith ; 



dots represent the nOW b, wood; c, region of growth (cambium); 

 Closed Channels (fibrO- d cortex > e epidermis ; f, lenticel. 



vascular bundles) 



along which the fluids passed to and from the leaf. 



In the lower portion of the twig in place of buds we 

 observe short side twigs. These are paired, and generally 

 are miniature representations of the main twig. They 

 stand in the same position as do the buds, and have leaf 

 scars below them ; they themselves have small paired buds 

 with leaf scars and a terminal bud. 



Just above the place where the first (counting from the 

 tip) of these side branches come out, the main twig shows 

 a number of close set ring scars. These^ are evidently the 

 scars of a number of leaves (scale leaves). On a long twig, 

 if we trace backward from the tip, we find that ring scars 

 of this type occur at regular intervals, although they 

 become less distinct with age. Pupils on reflection may 

 be able to suggest that these ring scars mark the position 



