STRUCTURE OF THE STEM 



93 



peculiar pits. These pits, when young, are shaped much 

 like two perforated watch-glasses, placed against a piece 

 of cardboard, with their concave sides toward each other 



FIG. 63. FIG. 64. 



FIG. 63. Part of a Sieve-Tube from Linden. 

 *, sieve-plates on the cell- wall, (x about 900.) 



FIG. 64. Parts of Sieve-Tubes as found in Plants of the Gourd Family. 



(Greatly magnified.) 

 s, s, a sieve-plate seen edgewise ; above it a similar one, surface view. 



FIG. 65. Cross-Section of Fir Wood. 

 s, a resin passage ; m, medullary rays. (Much magnified.) 



