440 Scientific Proceedings. Royal Dublin Society. 



thick), e.g., in Colombian mahogany [Cariniana pyriformis (PL XXV., fig. 22), 

 or they may attain 8 to 10 cells in thickness, e.g., Sapeli (PL XXXIII., fig. 67), 

 Khaya senegalensis (PL XXX., fig. 49), Swietenia mahagoni (PL XXII., 

 fig. 1), &c. Sometimes the laminae viewed on cross-sections form curves 

 uniformly convex on the outside, sometimes there are salients on these curves, 

 and sometimes concavities. The cells of the laminae are usually empty, but 

 sometimes are filled with dark contents. In Colombian mahogany about one- 

 third of the thin-walled parenchymatous cells of the laminae are filled with 

 opaque contents, and a very striking appearance is presented. Sometimes a 

 copious deposit is laid down between the cells of the laminae, and accumulates 

 in special intercellular lacunae. These lacunae are cylindrical, with their 

 longitudinal axis parallel to the vessels of the wood, and may be very close to, 

 or even in contact with, one another tangentially. Such laminae, with their 

 intercellular lacunae, give rise to dark lines in cross and radial sections and 

 in tangential sections to irregular bands, bordered or fringed on each side by 

 the light-coloured layers of the laminae. The cells adjoining the lacunae are 

 flattened and regularly arranged (PL XXX, fig. 49, PL XXXVIII. , fig. 97, 

 PL XXXIX., fig. 108). These markings often greatly emphasize the figure 

 of the wood. 



The spacing of the laminae is also various, and sometimes affords an 

 important diagnostic. Thus the laminae may be spaced fairly uniformly and 

 closely (0 - 2 mm. to 0'5 mm. apart), as in Colombian mahogany (PL XXV., 

 fig. 22,1, where they remind one of the similar structures in the walnuts and 

 hickories. This is also the rule in Guatemalan (fig. 40) and Sapeli (figs. 67 and 

 70) mahoganies, Dyaoxylon lessertianum (fig. 109), &c. Again, the laminae may 

 be quite irregularly spaced, but moderately distant from one another (0'5 mm. 

 to 25 mm.). This is usual in Swietenin mahagoni, S. macruphylla, and C'edrela 

 odoratn (PL XXII., fig. 1, PL XXIII., figs. 7, 10j. In some mahoganies 

 (Khaya spp. and Gaboon mahoganies) the laminar parenchyma may be absent 

 over great thicknesses of the wood, and appears to be distributed quite irregu- 

 larly. British Guiana or Demerara mahogany {Carapa guianensis) presents the 

 peculiar case that in some specimens moderately spaced laminae are visible, 

 while in others they cannot be made out with caref id lens examination. Possibly 

 here we have to do with two species of Carapa (PL XXIV., figs. 13 and 16). 



The laminae are usually quite independent of one another right round the 

 circuit of the wood, but they occasionally run into and join up with one 

 another. Again, they sometimes appear quite independent of the vessels, and 

 they may traverse the denser region of the growth- zones or be situated in the 

 less dense. Sometimes they seem to connect the vessels (or circumvasal 

 parenchyma) tangentially, and sometimes they mark the limit of the growth- 

 zones. In some woods the parenchymatous laminae are crowded more closely 



