68 



JElkins and Wieland — On Devonian Wood. 

 Figs. 2-5. 



Fig. 2. Transverse section of wood showing two growth rings, g. m, 

 medullary rays. The cellular structure of the medullary rays is not shown, 

 as the cell walls are seen only with difficulty. Eesinous tracheids occasional. 

 The rows of tracheids marked t are probably near their terminations, hence 

 of smaller diameter than the neighboring cells. (See similar cells in photo- 

 micrograph 1.) Note the isolated cells with shortened radial diameters, x 30. 



Fig. 3. Radial section of wood showing rays and tracheids. Note the 

 contents of the tracheid to the left. The pitless appearance of parts of 

 tracheids is due to extreme thinness of section, both radial walls being cut 

 awav. A growth ring five cells broad traverses the middle of the figure, 

 x 50 ± . 



Fig. 4. Radial section of wood more highly magnified than fig. 3. The 

 presence of a growth ring tracheid is indicated by single rows of pits in 

 tracheid in midfield. The pits in the lower part of tracheids were cut away. 

 The medullary ray is six cells in height, but only two rows of ray cells are 

 shown, x 140. 



Fig. 5. The same as fig. 4. Showing series of tracheids cut near termina- 

 tion and including a growth ring to the left, x 140. 



