THE VEGETATIVE ORGANS OF PLANTS. 



271 



of the bast or inner bark of our common trees; those 

 nearest the centre of the stem, c, are loood-cells. In the 

 maize stem, bast and wood-cells are quite alike, and 

 are distinguished only hj their jDOsition. In other plants, 

 they are often unlike as regards length, thickness, and pli- 

 ability, though still, for the most part, similar in form. 

 Among the ■wood-cells we observe a number of ducts, d, 

 €, y, and between these and the bast-cells is a delicate and 

 transparent tissue, g, which is the cambium — in which all 

 the growth of the bundle goes on until it is comjolete. On 

 d, e £ — ff A . « , ,, 



Fig. 49. 



either hand is seen a remarkably large duct, 5, b, while the 

 residue of the bundle is composed of long and rather 

 thick-walled wood-cells. 



Our understanding of these parts will be greatly aided 

 by a study of fig. 49, which represents a section made 

 vertically through the bundle from c to h, cutting the va- 

 rious tissues and reveaUng more of their structure. In this 

 the letters refer to the same parts as in the former cut : 

 «, a, is the cell-tissue, enveloping the vascular bundle ; 

 the cells are observed to be much longer than wide, but 

 are separated from each other at the ends as well as sides 

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