104 PRACTICAL BOTANY 



structure as those in Pinus. These vessels are usually 

 of large cavity. 



(iii.) Vessels with both pitted and reticulate 

 marking, superposed on one another on the same 

 lateral walls: these vessels usually occur in groups, 

 and are of small bore. 



Note in all these, but especially in (iii.), points wheiw 

 transverse or oblique septa have been partially or 

 completely absorbed. 



I. Fibrous cells,, which occur in large groups, 

 between the vessels : they are long, and prosenchyma- 

 tous, and are intertwined, so that it is difficult to follow 

 them through their whole length. They have little or 

 no cell-contents, and their walls are not pitted. 



c. Xylem-parenchyma : oblong cells with pro- 

 toplasmic contents, and starch : walls thick, lignified, 

 and pitted : they occur in longitudinal bands : note 

 their close contact on the one hand with medullary 

 rays, on the other with vessels. 



Examine the medullary rays in the xylem : they 

 are composed of oblong cells, with their longer axes 

 horizontal, arranged like bricks in a wall : in characters 

 they resemble xylem-parenchyma. 



8. The pith presents in radial section, for the most 

 part, the same characters as those already noted in 

 transverse section. 



VI. Treat some small pieces of the wood of the Elm 

 with a small quantity of Schulze's macerating fluid 

 (see Appendix A) in a test tube, and warm gently till 

 the tissues break up, and the several constituents begin 

 to separate : then wash with water, and mount a very 

 small quantity in water or glycerine. 



