GEOLOGY AXD PALEONTOLOGY OE THE CANAL ZONE. 31 



larger, more generally compound, and closer together, and in other 

 zones they are more distant, slightly smaller, and prevailingly single. 

 No changes are observable in the other elements and there is no 

 regular alteration of vessel rich and vessel poor areas nor any change 

 from so-called summer to spring wood such as characterizes the trees 

 of the temperate zone. 



Vessels single or two, three, or four together in radial rows (an 

 anomalous group of five vessels in juxtaposition is shown in the de- 

 tailed drawing) . Outline of single vessels elliptical, those in groups 

 flattened on one or both sides by mutual compression ; their tangen- 

 tial diameter ranging from 0.10 mm. to 0.14 mm.; their radial diam- 

 eter ranging from 0.12 mm. to 0.16 mm., exceptionally large ones up 

 to 0.22 mm. ; their walls thick, 0.0067 mm. to 0.01 mm. in thickness, 

 clearly showing the numerous small pits in section. Vessels fre- 

 quently filled with gum. Vessels usually surrounded by one to three 

 layers of rounded or more or less compressed thin-walled wood paren- 

 chyma, somewhat variable in amount in different parts of the stem 

 and tending to form tangential bands. Prosenchyma very abundant, 

 the elements polygonal, small, somewhat smaller than those of the 

 wood parenchyma, and thick walled. Rays very numerous, one or 

 two cells wide as seen in transverse sections, flexuous in their courses 

 since they are bowed out around the large vessels and approach more 

 or less in the radial intervals between vessels; from 0.10 mm. to 

 0.20 mm. apart, averaging nearer the former than the latter figure. 

 The ray cells toward the ends of the rays which appear to be those 

 usually seen in the several sections examined are not elongated radi- 

 ally but are nearfy isodiametric and about 0.02 mm. in diameter. 



Radial section. — The radial section shows the close set, fine, trans- 

 versely elongated pits of the vessels which have simple perforations. 

 The wood parenchyma is septate, the cells being about 3-| times as 

 long as wide with large simple pits. The rays are of variable height, 

 from 9 to 17 cells. They are seen in radial view to consist of a central 

 series of radially elongated cells with numerous fine simple pits, 

 above and below which is a series of longitudinally elongated cells, 

 beyond which are one or two rows of isodiametric cells which are 

 regularly hexagonal in this view. 



Tangential section. — The tangential section shows the uniform 

 close set fine pitting on all the walls of the vessels, the relative short 

 length and the large simple pits of the adjoining septate wood paren- 

 chyma. The rays are seen to be very numerous, and separated by 

 but few rows of flexuous prosenchyma ; they are lenticular in outline 

 and of variable height, one or two rays of terminal cells (those which 

 are hexagonal in outline in the radial view) are single; then come 

 one to three biseriate rows (those longitudinally elongated in the 



