Note, false ring-effects, partial, only due to climatic factors, or to adjustment of 

 growth-curvatures in axis. Strong leading shoots may be 1 2 mm. diam. at end of 

 first year, and show tracheides 20 fx radially, and 100 in a radial row. In strong- 

 growing trees the annual rings may be 8 mm. broad. 



Longit. Radial Sect, shows more particularly the pitted tracheides of the xylem, 

 and the sieve-tubes of the phloem : also giving clearer view of rectangular cork-cells ; 

 phloem of elongated sieve-tubes crossed by ray-parenchyma; metaxylem of pitted 

 tracheides crossed by med. rays; pith of elongated cells with distinct simple pits. 

 Fresh material differentiates well in Chlor. Zn. Iod.,and in Phloroglucin-25 % H 2 S0 4 ; 

 Note especially : 



(1) Sieve-tubes greatly elongated, with pointed ends (both ends not seen), 10 fx 

 wide, with non-cellulose areas as oval spots (6 ^,) on radial wall facing, as sieve-areas 

 (cf. white spots on deep-blue wall in Chor. Zn. Iod.). 



(2) Pitted tracheides, about 15 /x wide, with pointed or irregularly wavy 

 rounded ends (both ends not seen) ; bordered pits as exact concentric circles (outer 

 12 fx diam.), in scattered single series, on radial wall facing only. Characteristic 

 details of Medullary Rays preferably seen in older material. 



III. In older well-grown stems, an inch in diam., note in transv. sect. : 



Annual Rings, in metaxylem, from 1-2 mm. wide, presenting marked 

 differentiation from spring-wood tracheides, 20-30 fx in radial direction; grading 

 to summer wood with radial width reduced to 10-6 fx, and thick lining wall 3 jx. The 

 contrast between the smallest last-formed summer tracheide, and the large spring 

 tracheide, gives the precision of the ring-effect ; but the appearance to the naked eye 

 is due to the dense mass of the summer wood (often up to half the width of the ring). 

 Single radial rows of tracheides may be traced across the growth of several years. 



Ring-effects are also shown in the phloem to a lesser extent : a vague line of 

 larger phloem-parenchyma being formed at the end of each season ; many such rows 

 may be in sight before being wholly crushed out. These parenchymatous units are 

 long persistent, and store starch ; others tannin and calc. oxalate crystals as excreta. 

 The former divide to a certain extent to keep up with the growth of the stem, 

 and ultimately appear in the bark. 



In Rad. Longit. Sect, note characteristic details in Medullary Rays : 



(1) Medullary Ray Parenchyma (M.R.P.), of living cells, with cellulose 

 walls, 15-20 fx, and large nuclei; radially extended from 50 /x, summer, to 180 fx in 

 spring wood ; the nuclei being oval and radially elongated also (30 /x) ; hence crossing 

 3-7 tracheides, with which they communicate by one large rounded pit each, or 

 broadly oval in spring-wood, and a diagonal flare in summer wood. The cells store 

 starch in autumn, but show none in summer (Aug)., and again only fat in mid-winter. 



(2) Medullary Ray Tracheides (M.R.T.), as units similarly elongated, but 

 definitely sclerosed, without contents ; the internal wall toothed and jagged, projecting 

 into the lumen ; and communicating with the pitted tracheides, and with each other, by 

 small bordered pits (10 fx): varying in length from 30-150 fx, and crossing 1-6 

 tracheides. Usually found in definite radial rows (no mixing) of 1-2 deep, along the 

 upper and lower margins of the M. Rays. The outer layer is more or less irregularly 

 extended, with sliding effects, vertically between the divergent tracheides, as in the 

 chinks opened up by the pressure of the living and turgid M.R.P. 



(3) In the Phloem the rays continue as living parenchyma, with conspicuous 

 contents and nuclei ; but the peripheral series again tend to vertical extension, with 

 characteristic effect in units of no great radial width. In winter the latter store 

 proteid, but starch is also present at autumn starch-maximum. These are distinguished 

 as albumen-cells, and are apparently utilized as ' companion-cells ' for the adjacent 

 sieve-tubes with which they communicate by lateral sieve-areas. 



In Tangential Section, cut across spring-wood, note the distribution and 

 vertical range of M.R., also tangential face-view of the tracheide-walls. Rays mostly 

 uniseriate, 1-15 cells deep; larger rays ('fusiform') include parenchyma and small 

 resin-duct. Cf. distribution of M.R.T. in the ray-margins ; bordered pits as seen 

 in section; special large pits of M.R.P. ; and pointed ends of pitted-tracheides 

 (1-2 mm.). In similar section through Phloem note large cells of M.R.P. and tannin- 

 sacs with Calc. Oxalate crystals. 



8 





