KEY TO THE WOODS OF THE BROAD-LEAVED TREES 

 INCLUDED IN THE COURSE 



Note. When the visibility of any tissue is in doubt, run down both alter- 

 natives. 



1. Woods having a pore-ring in the innermost part of the annual 

 ring (including those that have a scanty row of pores made 

 more visible by the parenchyma with which they are packed) 2 



1 a. Woods having no pore-ring 14 



2* . Pores of the Autumn zone arranged in radial streams or lines . 3 



2 a. Pores of the Autumn wood connected by parenchyma into festoons, 



lines, arcs, angles or scraps (tangentially or obliquely) . . 5 



2 b. Pores scattered, not joined by parenchyma, not even in the late 



Autumn wood 11 



3. Rays prominent in transverse section 4 



3 a. Rays obscure in transverse section Chestnut 



4. Wood with stripes of a pinkish or pinkish-brown colour: watery 



extract at first nearly colourless . . . American Red Oak 



4 a. Wood uniformly brown 25 



5. Pores of the pore-ring very much larger than those immediately out- 



side it in the Summer wood 6 



5 a. Pores of the pore-ring but little larger than those following . . 9 



6. Pore-ring of one row of pores only .... American Elm 



6 a. Pore-ring of more than one row 7 



7. Rays obscure and light- coloured: pores of the Autumn wood joined 



by parenchyma to short lines, arcs or angles, only . . Ash 



7 a. Rays brown, quite evident though small: pores in the Autumn 



wood in practically continuous, concentric lines ... 8 



8. The half-tone effect produced by the rays in tangential section. 



obscure: rays (microscope) appear of the shape of a slender 

 skiff (Fig. 11): reaction of watery extract with perchloride 

 of iron, golden, no precipitate (constant?) . ' Wych Elm 



8 a. Half-tone effect pronounced: rays in tangential section having the 



outline of a broad-beamed boat (see Fig. 10): watery extract 

 with perchloride of iron gives a slight brown precipitate 

 (constant?) Common Elm 



9. Parenchyma in tangential section (microscope), arranged alter- 



nately: wood whitish or greenish-white within . Mulberry 



9 a. Parenchyma in tangential section in palisade (see Fig. 12) .10 



10. Pores choked with thy loses which are visible with the lens: rays 



comparatively low in tangential section (microscope) (see 

 Fig. 12) False Acacia 



10 a. Thyloses few and difficult to find: rays high in tangential section 



(microscope): wood becomes very dark-coloured . Laburnum 



11. No minute bars of parenchyma between ray and ray . . .13 



11 a. Cross-bars present (sometimes very difficult to find) ... 12 



12. Cross-bars of parenchyma very clear and unmistakable . Hickory 



* Note that there are more than two alternatives here. 



48 



