FIBRO VASCULAR TISSUES: PARENCHYMA 



43 



changes. They now show bordered pitting instead of pores of the 

 simple type. The right-hand longitudinal segment in the figure 

 shows the region above that represented in the central segment. 

 Here the continuation of the parenchymatous elements of the 

 median segment is below, and this type of cell is again merged into a 

 series of short tracheids derived from the segmentation of one of 

 the normal longitudinal elements of the wood. 



\9 



FIG. 33. Longitudinal section of the wood of the root in Picea canadcnsis. 

 Explanation in the text. 



The general situation in regard to the mode of origin of longi- 

 tudinal storage elements or wood parenchyma in the gymnosperms 

 can perhaps be more readily illustrated by means of a diagram. 

 Fig. 34 represents a ray, ordinary tracheids, and a septate or 

 divided tracheid in relation to one another in the longitudinal 

 aspect. The ray need not be specially considered, as the subject 

 of the origin and organization of rays is to be discussed in the 

 following chapter. Turning our attention to the normal tracheids 

 represented in the diagram, we find it clear that these are char- 

 acterized by the possession of pits both on the radial and on the 



