24 THE WHITE PINE. 



The frequency of seed year* varies of course not only o^i account of more or less favorable seasons, 

 but according to locality and climatic conditions^ In Europe the White Pine is regarded as a 

 frequent and heavy seeder, one year out of three being generallyujjxrfiuctive. A grove of 8 acres 

 near Frank tort rathe Main produced during twenty years, on an average, 8100 worth of seed, 

 with a maximum yield of $500, and with but three "off" or fail years in the twenty. Similarly 

 an area of about 4<> acres in the Palatinate furnishes as high as 1,700 bushels of cones, or about 

 |N>uiids of seed, supplying all the nurseries of the Palatinate State forests with seed. 



THE WOOD. 



The structure and development of the wood of the White Pine may be studied to the best 

 advantage by beginning with a young shoot cut from a vigorous tree in early summer. A cross 

 >ection of such a shoot in the first season of its growth (PI. VII, l) shows three plainly marked 

 zones the pith (m) surrounded by the wood (x) and the inner bark (ph), which together form 

 the conspicuous /one crossed by radiating bands, the so-called medullary rays, and outside of the 

 parts just described, a broad zone of cellular tissue, constituting the middle bark, which is bounded 

 externally by the epidermis. 



The pith, medullary rays, and middle bark consist of simple cells, originally of an irregularly 

 rounded form. Together they constitute the so-called ground tissue of the stem, as distinguished 

 from the fibro-vascular portion, which includes the wood and inner bark. 



Within the cortical portion of the ground tissue numerous large openings (PI. VII, 1, rd) are 

 seen, of different sizes and apparently without definite arrangement. These are the resin ducts. 

 Kadi duct runs longitudinally through the stem, and consists of a central cavity filled with resin, 

 around which is a single layer of secreting cells, easily distinguished by the nature of their con- 

 tents from the. surrounding cells of the cortex. At this stage of development the resin ducts are 

 confined to the cortical parenchyma, none having yet been formed in the woody portion of the 

 stein; but later in the season, as may be seen iu older sections, a number of ducts are formed, 

 arranged in a circle near the periphery of the wood. These have essentially the same structure 

 as those of the cortex, but are of smaller size and are surrounded by fewer secreting cells. Iu 

 cross sections of older stems the resin ducts are seen, arranged iu an irregular circle, in each 

 annual ring. Their physiological significance is not fully understood, though there can be little 

 doubt that De Vries is correct in assuming that the abundant resin is of service to the growing 

 tree, when wounded, in preventing decay of the wood, and that its preservative influence is con- 

 tinued after the tree has been cut into lumber. 



In such a young shoot as has been described the cells are vitally active, and are filled with 

 granular protoplasm, in addition to which several other substances are either produced or stored 

 up in them, particularly in the cells belonging to the ground tissue. Chlorophyll occurs in the 

 pith and medullary rays as well as in the cortical portion. It is most abundant in the cells of the 

 cortical parenchyma, occurring in the form of minute grains, irregular iu shape and size. Starch, 

 in rounded granules, occurs abundantly throughout the ground tissue, the cells of the cortex con- 

 taining a larger proportion than those of the pith. Resin, as already stated, fills the resin ducts 

 and the secreting cells around them, though starch is often found in the latter. 



Passing now to the woody portion immediately surrounding the pith, two characteristic fea- 

 tures at once attract attention. The elements composing the wood, ,r ( PI. VII, 1 and 3), have a 

 much narrower lumen than those of the pith, and are regularly disposed in radiating rows. These 

 dements, the tracheids, are elongated thick-walled cells, four to six sided, according to the number 

 of traehfids by which they are surrounded. Their walls are lignified and are marked by the 

 peculiar structures called bordered pits. Their structure, when fully developed, is shown in PI. 

 VIII. /..?, and /. In the economy of the tree the wood fulfills the function of mechanical support, 

 and serves as the conducting tissue through which the water, evaporated from the leaves, is carried 

 up from the roots. 



'I lie medullary rays are composed of cells so flattened by the pressure of the tracheids that 

 on longitudinal sections they appear as represented in PI. VIII, 3. They contain a conspicuous 

 nucleus, are closely packed with granular food substances, and serve collectively as a storehouse 



