SCOTS PINfi. 



(3) The phloem parenchyma cells, arranged in longi- 

 tudinal rows and with abundant contents. 



(4) The brown phloem cells with crystals. 



(5) The phloem portions of the medullary rays, in 

 which the middle cells (" starch-cells ") contain starch- 

 grains, the upper and lower cells (" albuminous cells ") 

 protoplasm but no starch as a rule ; these cells have very 

 large nuclei and are often elongated longitudinally and 

 closely applied to the sieve-tubes. 



(6) The cambium, consisting of long thin- walled cells 

 with abundant protoplasm and long narrow nucleus. 



(7) The rays running through the cambium and show- 

 ing here the same features as in the phloem, but the upper 

 and lower cells changing in character on reaching 



(8) The xyleni, where they apparently run across (in 

 reality between) the tracheids and have their upper and 

 lower cells empty (" tracheidal cells ") and the middle 

 cells (" starch cells ") with protoplasm and usually also 

 starch ; some rays show only one of these two kinds of 

 cells, or tracheidal cells may occur in the middle of the ray 

 if the latter is rather deep. 



(9) The bordered-pit tracheids, making up the bulk 

 of the xylem, and seen as long narrow cells with oblique 

 pointed ends, each bearing on the radial walls a single row 

 of bordered pits, each pit appearing as two concentric 

 circles. 



(10) The annual rings, shown by the narrower and 

 thicker-walled autumn tracheids as contrasted with the 

 wider and thinner- walled spring tracheids. 



(11) The narrow spiral or annular protoxylem tra- 

 cheids, lying nearest to 



(12) The pith, which consists of parenchyma cells 

 some with cellulose pitted walls, protoplasms, and nucleus, 

 others with lignified pitted walls but no contents. 



521. Now cut successive Tangential Longitudinal 

 Sections (Fig. 91) through (A) the Phloem, (B) the 

 Cambium, (0) the Xylem in each case, of course, only 

 the middle portion of the section will be strictly tan- 

 gential, i.e. at right angles to a radius of the stem. 



