26 THK WHITE PINE. 



ml are tbi-rwfore termed the outer cell*; the other kind makes up the intermediate rows and are known as the 



inniT cell*. 



In the appearance of Ixith outer and inner cells then- is :\ marked and constant ditVerence in different groups 

 of pine-t. While the interior of the wall of the outer cells (transverse traoheids) is smooth in some groups, it is 

 bvttt with nniiiiToiii bold projections in others. Similarly the inner cells (parenchyma) of the spring wood of each 

 ray in some groups have Init n single large pit comninnicating with the neighboring tracheid, while in other groups 

 this is brought about by three to six smaller pits. 



Based upon these differences, the following classification of the wood of different species of pines is proposed 

 by Dr. J. Schroeder: 1 



SECTION I. Walls of the tracheids of the pith ray willi dentate projections. 



a. One to i wo large, simple piU to.each tracheid on the radial walla of the cells of the pith ray. Group 1. Represented In this country 



only 1>> I'. trtinoM. 

 fc. Three to six simple pits to each trachcid, on the walls of the cells of the pith ray. Croup 2. /'. tMda. j/aluitru, etc., including 



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

 SECTIOM II. Walls of tracheids of pith ray smooth, without dentate projections. 



ii. Dneor two large pits to each tracheid on the radial walls of each cell of the pith ray. Group :t. /'. iirubut. lambertiana, and other 

 true White Pines. 



b. Throe to six small pits on the radial walls of each cell of the pith ray. .-Group 4. P. parryana, and other nut pines, including also 



I*. 6n//otfr<ina. 



Returning to the medullary ray of the White Pine, it i observed that the walls of the outer cells arc thin 

 (1.5^ to 2 >i); the round pits quite variable in number and size, but always as small, and often smaller, than the 

 pits of the tracheids in the summer wood; also tliat the walls of the inner cells are thin (1.5 /* to 3 ft), 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 the 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 n ; the width was found to be about 7 for the outer and 12 ft 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 ft for outer 

 and inner cells. The average number of cell rows in one medullary ray, for the specimens studied, is 7.5, whereof 

 2.6 fall to the outer cells and 4.9 to the inner cells. The limits of the total number of cell rows were 2 and 16; the 

 height of the ray, therefore, 46 // to 368 /<, dimensions scarcely appreciable to the unaided eye. What is lost in size 

 is gained in number; on an average 21.3 medullary rays were counted on 1 square millimeter, or 13,:U2 to 1 square 

 inch of tangential section. 



A study of the wood iu its physical and mechanical properties, by Mr. Filibert Roth, will be 

 found further on in this monograph. 



EXPLANATION OF PLATE VII. 



1. 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, both of which are traversed radially by the medullary rays. The thick 

 cortical parenchyma outside of these is marked by the presence of a number of large resin dncts. 



2. Portion of epidermis, with appendages. Beneath the epidermis a few cells of the cortical parenchyma containing 



starch. 

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



thin-walled cells composing the cambium lying between them. 



[Figs. 2 and 3 were drawn with great care with the camera, but unfortunately no statement of the magnification 

 was preserved with them.] 



EXPLANATION OF PLATE VIII. 



/. Cross section of wood X 175. The section includes parts of three medullary rays, the middle one of which is cnt 

 partly through the 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 right. 



2. Radial longitudinal section of wood x 200, showing a few of the thick-walled tracheids of the summer wood 



followed by the large thin-walled ones of the succeeding spring, both crossed by a medullary ray. The 

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

 the simple pits of the inner cells. 



3. Tangential section of wood x 200. 



4. Cross section of part of twig collected May 20, 1886, x 175, showing cambium and development of wood and bark. 



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



GROWTH AND DEVELOPMENT. 



The seeds of the White Pine retain their vitality for a long period. Trustworthy observers 

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

 germination and successful growth are, in general, the same as for other pines, namely, a suitable 



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



