448 Scientific Proceedings, Royal Dublin Society. 



Rays, l-,2-, 3-, 4-, 5-ply. In some cases 5-ply and even 4-ply rays are absent. 

 Margin 1 or 2 cells deep, sometimes with crystals; distinct from the inner 

 cells, which are usually considerably smaller. 



R.S. Fibres septate or non-septate, frequently bent at nearly right angles, 



in contact with margin of rays. -Cells of ray-margins iso-diametrical or 

 elongated horizontally, rarely elongated vertically, often containing crystals. 



2. Swietcnia rnacrophylla. 



No. 49 from commercial source, labelled "Baywood." 



No. 82 „ ,, ,, " Honduras mahogany, Belize." 



No. 87 „ „ „ "Tabasco mahogany." PI. XXIII., 



figs. 7, 8, and 9. 



No. 88 from commercial source, labelled " Tabasco mahogany." 



No. 89 „ „ „ " Tabasco mahogany, Laguna de 



Terminos." 



No. 213 from commercial source, labelled " Colombian mahogany." 



Red brown to golden brown ; lustrous and roey. Fibres may be zoned in 

 dense and more open layers. Vessels sometimes zoned, often with black 

 contents, occasionally with white (calcium carbonate) contents. Paren- 

 chymatous laminae 1 mm.-lO mm. apart. Sp. gr. = - 65-0 - 43. 



C.S. — Vessels isolated or in small groups, M.T.D. = 0-20 mm.-0-.34 mm., 

 5-30 groups in 2-mm. field.— Fibres thin or moderately thick-walled. — Circum- 

 vasal parenchyma inconspicuous. Parenchymatous laminae 3-8 cells thick. 

 Scattered parenchyma absent or rare. 



T.S. — Pays fairly uniform in size, sides slightly bowed, finely tapered, 

 35-48 in 2-mm. field. Total width in 2 mm. = 0-40-0-50 mm. Height of rays 

 (average) = 0-45 mm.-0-60 mm. (5-30 cells). Average width = 0-030 mm.- 

 0-056 mm. (1-), 2-, 3-, 4-, 5-ply. Margin 1 or 2 cells deep, occasionally with 

 crystals. Middle cells angular and thin-walled. 



R.S. — Fibres septate, often bent at rays. Margin cells of rays square or 

 oblong, horizontal or vertical. 



Note. — No. 155 from the Colonial and Indian collections of the Imperial 

 Institute, London, labelled " Nicaragua, Nicaraguan mahogany." (PI. XXII., 

 fig. 6), and No. 233 from commercial source, labelled " Costa Rica mahogany " 

 are possibly from a different species of Swietenia. They differ from above 

 principally in having mostly non-septate fibres, and the rays seen in tangential 

 section have approximately parallel sides, and are abruptly tapered. 



