THE PRIMARY PERMANENT TISSUES 



33 



origin from strands similar in appearance to procambium strands 

 that have arisen from vertical division of the cells of the ground 

 meristem or protoderm. In the latter instance they would be 

 classified with the epidermis from the standpoint of their origin; 



FIG. 15. Diagram showing stages in the development of collenchyma. stone cells, 

 and bast fibers. A, collenchyma; i and 2, cross and longitudinal section of a collenchyma 

 cell in its primary meristem condition; 3 and 4, longitudinal and cross-sections of the same 

 cell at a later stage, the walls in 4 have commenced to thicken at the angles; 5 and 6, longi- 

 tudinal and cross-sections of a mature cell. The arrows indicate the planes through which 

 the longitudinal sections were cut. The stippling inside the walls indicates the protoplasts. 

 B, stone cells; i, in the primary meristem condition; 2, the cells have enlarged and the walls 

 have begun to thicken and become pitted; 3, the walls are completed. The priinary wall is 

 black, cellulose additions white, and the lignified walls in 3 are stippled. Notice that the 

 protoplasts have disappeared in 3, and the pits in some instances are branched; C, bast 

 fibers; i and 2, cross and longitudinal sections of primary meristem cells that are to become 

 bast fibers; 3 and 4, the same at a later stage; 5, longitudinal section of completed bast 

 fibers. In 5 the stippling of the wall indicates lignification. Note that the walls. -have 

 become pitted and the protoplasts have disappeared from the fibers. 



but on account of their position they will here be included With 

 the primary cortex. In their procambium-like state the bast fibers 

 are thin- and cellulose-walled and vertically elongated; proceed- 



3 



