26 THE WHITE PINE. 



null are therefore termed the outer cells: the other kind makes iij) llie iiitennediato rows .ind nre known as the 

 inner celU. 



In the appoiiranoe of holh outer ami inner cells there is a marked and constant dillVrence in dill'ereut groaps 

 of jiiues. While the interior of the wall of the outer cells (transverse tracheids) is smooth in some gronps, it is 

 beset with numerous bohl proji'ctions in r)tliers. Similarly the inner cells (i)ari>nchyma) of the sprinj; wood of each 

 ray in some j;ronps have lint a siujjlo lar;j;e pit comniuiiiiatin;;; with the iiei;ililiorin}i tracheid, wliile in otiier ;;roiip8 

 this is brought about liy tliree to six smaller pits. 



Kased upon these differences, the following classification of the wood of dift'erent species of pines is proposed 

 by Ur. J. Schroedor:' 



Section I. Walls of the tracheids of the pith ray witli dentate prnjoctions. 



a. One to two largo, simple pita to each tracheid ou the radial wallt* of the c«-lls ot the i)iili ray. — (Jroup 1. Itepn-aented in this country 



only h> /'. rt'titiosa. 



b. Xliree to six simple pits to each tracheid, on the walls of the cells of the pith ray.— tiroup 2. /'. taoda, palustrit, etc., including 



most of our "hard" and "yellow" pines. 

 Section II. W.ills of tracheids of jtith ray smooth, without dentate jirojections. 



o. One or two larije pits to each tracheid on tin- radial walU of each ci^U of the pith ray. — Group .'f. /'. xtrohug, Inmhcrtiana, am] other 



true "White Pines. 

 6. Three to six small jilts on the r.adial walls of c;u:h cell of the jiitli ray — (Iroup 4. /'. parrtiana, and other nut jiines. includini; also 



P. bal/ouriana. 



Returning to the mednllarv ray of the White I'ine, it is observed that tlie walls of the outer cells are thin 

 (1.5 // to 2 fi); the round pits quite varialdo in nnmber and size, but always ,is small, and often smaller, tlian the 

 pits of the traclieids in tlie liummer wood; also tliat the walls of the inner cells are thin ( 1..5 ii to 3 /;), for the most 

 part very thin, being largely occupied by pits; that the pits are large ovals on the radial walls of the cells in the 

 spring wood, small erect ovals in tlio summer wood, and small and irregular in outline above and below where the 

 inner cells communicate with each other. The length of these cells varies, even in the same ray, between 50 /< and 

 300 // ; the widtli was found to be about 7 « for the outer and 12 // for the inner cells; the height, more variable in 

 the outer than in the inner cells, and less variable than either width or length, may be set at about 23 /i for outer 

 and inner cells. The average number of cell rows in one medullary ray, for the specimens studied, is 7..">, whereof 

 2.C I'all to the outer cells and 1.9 to the inner cells. The limits of the total number of cell rows were 2 and 16; the 

 height of the r,iy, tliercforo, 46 « to 368 /(, dimensions scarcely appreciable to the unaided eye. What is lost in size 

 is gained in number; on an average 21.3 meilullary rays were counted ou 1 sipiare millimeter, or 13,:fl2 to 1 siiuare 

 inch of tangential section. 



A study of the wcxnl in its i)liysieal and niecbaiiical ])roperties, by Mr. Filibert Eotb, will be 

 found fiirtliiT on in tlii.s mouograpb. 



EXPLANATION OF I'l-ATB VII. 



/. Transverse section of fresh shoot, cut in summer of first year x 25. The zone of small cells surrounding the pith 

 includes the wood and inner bark, botli of which are traversed radially by the medullary rays. The tliick 

 cortical parenchyma outside of these is marked l)y the presence of a number of large resin ducts. 



-'. Portion of epidermis, with appendages. ISeneath the epidermis a few cells of the cortical parenchyma conlaiuing 

 starch. 



3. Highly magnified view of .i part of the transverse section, showing the structure of wood and inner bark, with the 



thill-walled cells composing the cambium lying between them. 



[rigs, 2 and 3 were drawn with great care with the camera, liut unfortunately no statement of the magnilication 

 was preserved with them.] 



K.XPLANATIUN OF I'LATE VIII. 



1. Cross section of wood x 175. The section includes parts of three medullary rays, the middle one of which is cut 



partly througli tlur inner cells and partly through the cross tracheids. The gradual transition from spring to 

 summer wood is clearly shown. Part of a resin duct is seen on the riglit. 



2. Radial longitudinal section of wood X 200, showing a few of the thick-walled trachi'ids of the summer wood 



f(dlowed by the large thin-walled ones of the succeeding siiring. lioth crossed by a medullary ray. The 

 liordered pits of tlie outer cells of the ray, shown both in section and surface view, are in strong contrast with 

 the simple pits of the inner cells. 

 5. Tangential section of wood x 2(X(. 



4. Cross section of jiart of twig collected May 20, l»8t), X 175, showing camliium and development of wood and bark. 



The woody ring is about one-third its final thickness. 



GROWTH AND DEVELOPMENT. 



Tbe seed.s of tlic Wliite Pine retain tlieir vitality for a long period. Trustworthy observers 

 state that a fair percentage will grow after being kept live years or more. The conditions of 

 germination and successful growth are, iu general, the same as for other i)ine8, namely, a suitable 



'Dr. J. .Schroeder, Das Holz der Conifcren, 1872. 



