STRUCTURE OF STEMS 



53 



hence the term vascular. If a young corn stalk or other leafy 

 stem is cut and the cut end placed in red ink or in a solution of 

 a red analin dye like eosin, the colored liquid rises in these bundles 

 and colors them, while the pith or other parts remain uncolored. 



rm 



Fig. 51. 



A , cross section of the stem of an oak tree thirty-seven years old, showing the annual 

 rings, rm, the medullary rays; m, the pith (medulla). B, cross section of the stem of a palm 

 tree, showing the scattered bundles. 



93. The palm stem. Palm trees are also monocotyledons. 

 In fig. 51, B, is shown a cross section. The arrangement and 

 distribution of the fibro-vascular bundles is similar to those in 

 the corn. 



94. Microscopic structure of the corn stem. A micro- 

 scopic study of a cross section of a corn stem shows that the 

 pithy portion is made up of quite large cells with thin walls, the 

 cells being equal in diameter. This kind of tissue is called 

 parenchyma. In the nbro-vascular bundle there is a great variety 

 in the size of the cells. Near the center of the bundle is a group 

 of small cells with thin walls filled with protoplasm if the bundle 

 is not too old. This group of cells is the cambium portion of the 

 bundle. This is the growing part of the bundle so long as 

 growth takes place. It is the region where the cells divide and 

 multiply in number, i.e., growth by division and multiplication, 

 and should be distinguished from those cells which have ceased 

 to divide, but grow by enlargement. Upon one side of the bundle 

 are seen the large vessels with the smaller fibers and some 

 thin-walled parenchyma cells. This is the woody portion of the 



