NATURE OF PLANTS 87 



furrows and seams that occur in the bark of most trees are caused 

 by the continued activity of the cork cambium and the cambium 

 of the vascular bundles which adds each season new cells to the 

 stem and so pushes out the cork cells. In this way it comes about 



FIG. 48. FIG. 49. 



FIG. 48. Cross-section of cells of bottle cork showing the delicate character 

 of cork cells. 



FIG. 49. Scale bark of pitch pine. The crescent-like lines in the bark 

 show the successive positions of the cork cambium. 



that the cork cells are pushed further and further from the center 

 of the stem and since they are not capable of dividing they are 

 pulled apart, forming the characteristic furrows in the bark. 

 It will often be noticed that the bark of some trees, as the cone- 

 bearing trees, sycamore, etc., cleaves off in shell-like scales. 

 This is due to the formation of a new cambium that joins on to 



FIG. 50. Cross-section of the outer part of a stem showing the early 

 development of a lenticel. Note the irregular character and loose arrange- 

 ment of the cells below the stoma and the cork cambium, c, extending out on 

 either side of the lenticel. 



the old cambium in the form of crescents (Fig. 49). Conse- 

 quently as this bark is pushed out it breaks along these successive 

 crescent shaped cambiums and finally cleaves off in scales. In 



