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BOTANY. 



The fibro-vascular bundles of the stem of the seedling plant show a 

 structure quite similar to that of the leaf, but very soon a difference is 

 manifested. Between the two parts of the bundle the cells continue to 

 divide and add constantly to the size of the bundle, and at the same time 



cam. 



two-year-old branch at the point where the two growth rings join : i, the 

 cells of the first year's growth ; n, those of the second year, m, a medullary 

 ray, x 150. D, longitudinal section of a branch, showing the form of the 

 tracheids and the bordered pits upon their walls, m, medullary ray, x 150. 

 E, part of a sieve tube, x 300. F, cross-section of a tracheid passing through 

 two of the pits in the wall (p), x 300. G, longitudinal section of a branch, 

 at right angles to the medullary rays (m). At y, the section has passed 

 through the wall of a tracheid, bearing a row of pits, x 150. H, cross-section 

 of a resin duct, x 150. /, cross-section of a leaf, x 20. fb. nbro-yascular 

 bundle, r, resin duct. J, section of a breathing pore, x 150. i, the air space 

 below it. 



the bundles become connected by a line of similar growing cells, so that 

 very early we find a ring of growing cells extending completely around 

 the stem. As the cells in this ring increase in number, owing to their 

 rapid division, those on the borders of the ring lose the power of dividing, 



