286 INTRODUCTION TO BOTANY 
The well-protected chlorophyll tissue is able to withstand 
severe cold and drought, and lives through periods that would 
kill deciduous leaves. The amount of leaf surface is compara- 
tively small, but pine leaves probably begin their work earlier 
in the season than deciduous leaves do, and continue their 
work later. 
270. New leaves and branches. When the growth buds open 
in the spring, the branch extends, the new needle leaves begin 
to elongate (fig. 22/)), and within a few weeks the leaves reach 
their full size. This new growth was started in the preceding 
summer and autumn, so that within the bud during the winter 
there were the very small stem and leaves of the next spring’s 
growth. The scales from the growth buds fall away and leave 
scars, by means of which the former position of the end of the 
stem may be located. Also, by observing these bud scars from 
the tip to older portions of the branch, the age of the branch 
and the rate of elongation may be determined. 
271. The branch and stem. From transverse sections of 
branches and stems of different ages their general structure 
may be observed.! Innermost is a small pith region, which in 
older stems is compressed until it is not usually noticeable. 
Around this is the woody tissue (rylem) of the fibrovascular 
bundles. The woody tissues are joined together in such a 
way as to form a solid woody cylinder. It is possible to de- 
termine the age of the twig approximately by counting the 
layers or rings of wood, except when two or more distinct 
growth periods occur in the same season. In such cases more 
than one ring would be formed in the same year. At the outer 
edge of the woody tissue is a thin layer of cells (rambinm) 
which separates the woody tissue (ryleim) from the outer tissue 
(phloém). ‘The cambium is actively growing tissue which pro- 
duces new wood within and new phloém without. The tissues 
outside the phloém which we need to notice are the green bark 
and the dead hark. Dead bark is constantly being formed from 
the green bark within. This results in making the dead bark 
1 A hand lens will enable students to observe these regions of the stem. 
