\ 
222 BOTANY. 
mass of cells, the pith (Jf), and an outer, the rind, or cor- 
tex (R), connected with one another by the broad rays 
between the bundles (Fig. 125). 
469, As the stem grows older, the cambium of the bundles 
keeps.on forming tissues similar to those already found in 
the bundle; in other words, the woody part of each bundle 
is increased on its outer side, and the bark part on its ¢nner 
side. In the mean time the cambium between the bundles 
gives rise to new bundles, which then increase in size in 
the manner described above. The woody part of the stem 
soon comes to have the shape of a cylinder, surrounded by 
a softer bark portion as a sort cf sheath. 
470, The stem grows in thickness in the warm part of 
the year, but stops its growth as cold weather comes on. 
The first growth in each year is most vigorous, the cells 
being larger, while those formed towards the end of the 
season are regularly smaller and ,smaller until activity 
ceases, This manner of growth produces the well-known 
growth-rings, so readily seen in a cross-section of any pine 
or spruce stem. As there is generally but one period of 
growth each year in the cooler climates, every growth-ring 
represents a year of the tree’s life; but it appears that oc- 
casionally there may be two periods of growth in a year, 
and consequently two growth-rings. 
471. Many members of this class have canals running 
through the tissues of their stems and leaves, in which a 
resinous turpentine is found. 
Practical Studies—(a) In the spring of the year collect a quantity 
of the staminate cones of a pine (Scotch or Austrian are very good), 
and preserve such as are not wanted for immediate use in alcohol. 
Collect at the same time the young ovule-bearing cones which are 
to be found upon the ends of the new shoots as ovoid bodies, 8 to 10 
mm. long by 5 to 6 broad. 
