THE STRUCTURE OF STEMS. 



223 



are, of course, continuous with those of the former 

 year, and so extend from the pith to the bark. The 

 woody bundles of the second year are more numer- 

 ous than those of the first year. If each newly-added 

 portion of the old woody bundle was undivided, there 

 would be the same number of medullary rays through- 

 out the growth of the stem. But, besides the medul- 

 lary rays that separate the primitive bundles, and ex- 

 tend from the pith to the bark, there arise divisions 

 of each new bundle into two or three parts by series 

 of cells, which are called small medullary rays (Fig. 

 395). 



FIG. 395. 



In this figure, representing four years' growth, 

 you can trace the rays of each successive year. There 

 is only one of the first year's growth, and, by the de- 

 velopment of this portion of the stem, on the fourth 

 year you see fifteen. So that each year, with the for- 

 mation of the new woody layer, new medullary rays 

 are also started, which are prolonged on the following 

 years in the same way as the great rays proceeding 

 from the centre of the stem. 



