24 TIIK WniTE PINK. 



The frequency of seed years varies of (loiirse not (Mily on account of more or less favorable seasons, 

 but ;icc()i(liii}j t(i locality and climatic (conditions. In iMiropo tlic VVliite Pine is leparded as a 

 fre(iM('iit iihd licavy seei'.cr, one year out of tliice being generally i>rodnc,tive. A grove of >S acres 

 near Frankfort on tlio Main i)roduced during twenty years, on an average, *100 worth of seed, 

 with a tnaxinium yield of $')()(), and with but throe "oil'" or fail years in the twenty. Similarly 

 an area of about 40 acres in the I'alatinate furnislies as high as 1,700 busliels of <;ones, or about 

 1,.J00 pounds of seed, sui)plying all the nurseries of the Palatinate State forests with seed. 



THE WOOD. 



The strui'turo and develojimont of tlu! wood of the White Pine maybe studied to the best 

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

 section of such a shoot in the tirst season of its growth (PI. VII, J) shows three ])lainly marked 

 zones — the ])ith (in) surrounded by the wood (.r) and the inner bark (ph), which together form 

 the consi>icuous zone crossed by radiating bands, the so-called medullary rays, and outside of the 

 jiarts just describeil, a broad zone of cellular tissue, constituting the middle bark, which is bounded 

 externally by the ei)idermis. 



Th(! pith, medullary rays, and middle bark consist of simple cells, originally of an irregularly 

 roundecl form. Together they coiistituti^ the so-called ground tissue of the stem, as distinguished 

 from the tibro-vascular ])ortion, which includes the wood and inner bark. 



Within the cortical portion of the ground tissue numerous large openings (I'l. W I, 7, rd) are 

 seen, of ditVeieiit sizes and a]i])arently without definite arrangement. These are the resin duets. 

 ICaeh duct runs longitudinally through the stem, and consists of a central cavity filletl 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 paren(;hyiiia, none having yet been formed in the woody portion of the 

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

 arranged in a circle near the peri])hery 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 signific^auce is not fully understood, though there can be little 

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

 tree, when wounded, in preventing 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 describ(>d the cells are vitally active, and are filled with 

 gi'antilar protoplasm, in addition to which several other substances are either produced or stored 

 uj) 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 ])arenchynui, occuriing in the form of minute grains, irregular in slia])e and size. Starch, 

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

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

 and the sec-reting <;ells around them, though starch is often found in the latter. 



Passing now to the woody portion immcMliately surrounding the i)ith, two characteristic fea- 

 tures at once attract attention. The elements composing the wood, .r ( PI. VII, 7 and .?), have a 

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

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

 f)f tracheids by which thciy are surrounded. Their walls are liguificd and are marked by the 

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

 VIII, 1,2, and J. In the economy of the tree the wood fullills 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. 



The medullary rays are comi)osed of cells so flattened by the i)ressure of the tracheids that 

 on longitudinal sections they ajipear as Tejiresented in PI. VI II, .7. They contain a cous])icuous 

 nucleus, are closely i»aeked with granular food substances, and serve colle<;tively as a storehouse 



