218 PLANT ANATOMY. 
The tracheids (wood-cells) are prosenchymatous and likewise 
elongated cells, but these are far from attaining the length of the 
vessels. ‘Their walls are mostly pitted. In coniferous wood, 
which, as a rule, consists only of tracheids, areolated or bordered 
pits occur (Figs. 64, 72, 136). 
The last terminations of the nerves in leaves consist only of 
tracheids. The vessels and tracheids convey air and water; they 
form the conducting system for water and the inorganic nutri- 
ment. 
The wood-parenchyma is not necessarily present, but is de- 
oo 
Fia.' 135.—Vessels (fv) from Rhizoma Filicis, thickened in a scalariform manner 
(Berg). . 
_ veloped in many cases. In contradistinction to the prosenchy- 
matous, tracheal tissue, the former consists of thin-walled cells, 
which are connected with the neighboring vessels and cells of the 
medullary rays by means of pores, and are filled with various 
substances (protoplasm, starch, oxalate and tannin). The wood- 
_ parenchyma serves for conducting the carbohydrates and for the 
_ Storage of starch, and either traverses the vascular portion in 
____ the form of more or less isolated cells or occurs in the form of 
ae aay (Lignum Campechianum, Fernambuci, Guaiaci, San- 
Bee 2S ae at ; 2 aN j 
