130 BOTANY. 



leaves appear to grow directly from the main branch. Each 

 leaf is about ten centimetres in length and two millimetres 

 broad. Where the leaves are in contact they are flattened, 

 but the outer side is rounded, so that a cross-section is nearly 

 semicircular in outline. With a lens it is seen that there are 

 five longitudinal lines upon the surface of the leaf, and careful 

 examination shows rows of small dots corresponding to these. 

 These dots are the breathing pores. If a cross-section is even 

 slightly magnified it shows three distinct parts, a whitish 

 outer border, a bright green zone, and a central oval, colorless 

 area, in which, with a little care, may be seen the sections 

 of two fibro-vascular bundles. In the green zone are 

 sometimes to be seen colorless spots, sections of resin ducts, 

 containing the resin so characteristic of the tissues of the 

 conifers. 



The general structure of the stem may be understood by 

 making a series of cross-sections through branches of different 

 ages. In all, three regions are distinguishable ; viz., an outer 

 region (bark or cortex) (Fig. 76, A, c), composed in part of 

 green cells, and, if the section has been made with a sharp 

 knife, showing a circle of little openings, from each of which 

 oozes a clear drop of resin. These are large resin ducts (?). 

 The centre is occupied by a soft white tissue (pith), and the 

 space between the pith and bark is filled by a mass of woody 

 tissue. Traversing the wood are numerous radiating lines, 

 some of which run from the bark to the pith, others only part 

 way. These are called the medullary rays. While in sections 

 from branches of any age these three regions are recognizable, 

 their relative size varies extremely. In a section of a twig of 

 the present year the bark and pith make up a considerable 

 part of the section ; but as older branches are examined, we 

 find a rapid increase in the quantity of wood, while the thick- 

 ness of the bark increases but slowly, and the pith scarcely 

 at all. In the wood, too, each year's growth is marked by a 

 distinct ring (A i, n). As the branches grow in diameter 



