374 SCOTS PINE. 



phloem and the conjunctive tissue. Accordingly (5) the xylem 

 bundles appear to be embedded in a mass of uniform tissue. 

 (6) The xylem consists of from three to six radiating Y-sh a P e( i 

 plates, and between the outwardly-directed fork of each Y (P r - 

 toxylem) there is a resin-duct lined by epithelium. 



For transverse sections of successively older roots, use the roots 

 of older seedlings. Note that (1) the cortex becomes brown and 

 crushed, and is finally thrown off, owing to the activity of (2) the 

 cork cambium, which arises in the pericycle and produces (3) a 

 layer of cork ; (4) lenticels may be seen in some sections. (5) A 

 well-marked cambium is formed, beginning in the parenchyma 

 within the phloems, spreading round the protoxylems (outside the 

 resin-ducts), and producing internally (6) secondary xylem at 

 first in wedges, but later becoming continuous and showing annual 

 ring's as in the stem and externally (7) a continuous band of 

 secondary phloem. 



523. T. S. and L. S. of Bifoliar Spur. Get some young 

 dwarf-shoots (bifoliar spurs) and (1) cut transverse sections across 

 the lower part of the shoot, (2) cut off the two foliage-leaves close 

 to their bases and cut longitudinal sections of the shoot so as to pass 

 through the two leaves. In (1) note that the two leaves have their 

 flat inner (morphologically upper) faces in contact, their outer 

 (morphologically lower) faces being rounded, while each leaf shows 

 a sharp ridge on each side at the junction of the two faces. In (2), 

 if the section is exactly median, note the abortive growing tip of the 

 axis between the bases of the two opposite foliage leaves. 



524. T. S. of Foliage-leaf (Fig. 92). Cut trans- 

 verse sections from the middle of a leaf of the current 

 year; mount some unstained; treat some with iodine, 

 others with aniline sulphate. Note : 



(1) The semilunar outline of the section, with nearly 

 flat upper side and convex lower side. 



(2) The epidermis, a layer of thick-walled cells, covered 

 by a thick cuticle ; the cell-cavity is often nearly obliter- 

 ated, being very small and star- shaped owing to fine pits 

 which run out for some distance from the cavity ; on heat- 

 ing a section in potash, the cuticle itself is dissolved, 

 though it resists the action of sulphuric acid longer than 

 the other layers. 



(3) The hypodermis, with very thick and lignified walls, 

 showing fine canals (pits) ; this layer is in places two or- 

 even more cells deep, especially at the two ridges. 



