78 PRACTICAL BOTANY. 



contents. The form of the cambial cells may be better 

 studied in tangential sections; here it is difficult to 

 make it out. 



7. In the Xylexn (excluding for the present the 

 medullary rays), observe the following structures, all 

 of which have lignified walls 



(a). Vessels of various orders, which may be grouped 

 as 



(i). Spiral vessels (protoxylem) found at the central 

 part of the xylem, i.e. next the pith : they are usually 

 more or less disorganised, being often filled with thy loses. 



(ii). Pitted vessels, the lateral walls of which are 

 crowded with bordered pits, of essentially the same 

 structure as those in Pinus (p. 142). 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 where 

 transverse or oblique septa have been partially or 

 completely absorbed. 



(5). 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. Little or no cell- 

 contents : walls 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. 



