24 THK WHITE PINK. 



The frequency of seed years varies of course not only on account of more or less favorable seasons, 

 but according to locality and climatic couditions. lu Europe the White Pine is regarded as a 

 freijuent and heavy seet'.cr, one year out of thi-ee being gent-rally i)roductive. A grove of S acres 

 near Frankfort ou the ."Main ])roduced during twenty years, on an average, •'i' 10(1 worth of seed, 

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

 an area <>f about 40 acres in the I'ahUinate furnishes as high as 1,700 buslicls of cones, or about 

 1,300 pounds of seed, supplying all the nurseries of the I'ahitinate 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 sunnncr. A cross 

 section of such a shoot in the first season of its growth (I'l. VII, /) shows three jdainly marked 

 zones — the pith (w) surrounded by the wood (.r) and the inner bark {i>h), which together form 

 the consjiicuous zone 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 

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

 from the tibro-vascular iiortion, wliieii includes the wood and inner bark. 



Within the cortical portion of the ground tissue numerous large openings (PI. \'I1, 7, rdj are 

 seen, of difl'erent sizes and api)arently without definite arrangement. These are the resin ducts. 

 Each duct runs longitudinally through the stem, and consists of a central cavity tilled with resin, 

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

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

 confined to the cortical parenchyn'.a, none having yet been formed in the woody ])ortion of the 

 stem; but later iu the season, as maybe seen in 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. In 

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

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

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

 tree, when wounded, in i)reventing decay of the wood, and that its preservative intiuence 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 

 u\) in them, i)articularly in the cells belonging to the ground tissue. t!hloro])hyll occurs in the 

 pith and medullary rays as well as iu the cortical ])ortiou. It is most abundant in the cells of the 

 cortical parenchyma, occurring iu the form of minute grains, irregular in 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. Kesin, as already stated, fills the resin ducts 

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



Passing now to the woody portion immediately surrounding the ])ith, two characteristic fea- 

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

 much narrower lumen than those of thepith, and are regularly disposed iu radiating rows. These 

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

 of tracheids by which they arc^ surrounded. Their walls are lignilied and are marked by the 

 jjeculiar structures called b(udered jiits. Their structure, when fully developed, is shown iu PI. 

 VIII, 1,2, and J. In the economy of the tree the wood fulfills tlie function of mechanical support, 

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

 up from the roots. 



The medullary rays are comjjosed of cells so llattcued by the jtressure of the tracheids that 

 on longitudinal sections they appear as represented iuPl. VIII, 5. They contain a con.spicuous 

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



