246 soTAirr. 



of an inner mass of cells, the pith (M ), and an outer, the 

 rind, or cortex {E ), connected with one another by the 

 broad rays between the bundles (Pig. 146). 



461. 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 inner side. In the mean time the cambium 

 between the bundles gives rise to new bundles, which then 

 increa-se 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 of sheath. 



462. 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 toward 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 

 occasionally there may be two periods of growth in a year, 

 and consequently two growth-rings. 



463. 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 



