62 TUB OAK. 



ing of vessels and tracheids. They resemble tracheids, 

 but have very few and small, scarcely bordered, oblique, 

 slit-like pits : every stage can be detected between these 

 and true fibers. They must be looked upon as, so to 

 speak, abnormal, because their numbers are small com- 

 pared with the typical elements among which they 

 occur. 



The wood-parenchma consists of vertical groups of 

 short cells, each group having the fusiform shape of a 

 tracheid (Fig. 16, w.p) : hence the upper and lower cell 

 of each group has a, pointed end. Each group obviously 

 arises from the transverse divisions of a long, prismatic 

 cell, pointed at both ends a cambium cell. The trans- 

 verse section is round, and somewhat larger than that of 

 a tracheid, and the walls are somewhat thinner. Where 

 they abut on vessels and tracheids their walls have bor- 

 dered pits, but where they stand in contact with similar 

 groups, or with parenchyma rays, the pits are simple. 

 During periods of rest they are loaded with starch 

 grains. 



The length of the groups i. e., of the fusiform cells 

 cut up into short cells varies; the shorter ones have 

 only one transverse division. 



The wood-parenchyma is less abundant than the tra- 

 cheids and fibers, and predominates in the more vascular 

 parts ; after two to four or more fibers in a radial row a 

 single parenchyma cell may often be seen, but other ar- 

 rangements occur. In the parts where fewer vessels oc- 

 cur it is not uncommon to find a series of radial rows of 



