138 



General Botany 



in their position in the bark, and in their extent. Secondary 

 cambiums are in part responsible for the plate-like peeling of 



the sycamore and shagbark hickory, 

 and the knobs and ridges that oc- 

 cur on cork oak, cork elm, hack- 

 berry, and sweet gum. 



The monocot stem. The monocot 

 stem, like dicot and conifer stems, is 

 bounded externally by an epidermis 

 which closely resembles that of the 

 leaf. The groundwork of the stem 

 is made up of parenchyma, which is 

 commonly called the pith. The 

 parenchyma is usually composed of 

 thin-walled cells, and is the princi- 

 pal tissue in which the temporary 

 accumulation of foods occurs ; from 

 it the sugar solution is obtained 

 when the stems of sorghum and 

 sugar cane are crushed. In a mono- 

 cot stem the bundles are scattered, 

 instead of being arranged in a 

 cylinder as they are in a dicot stem. 

 In stems of grasses that are hollow 

 (Fig. 79) they are scattered through 

 the cylinder of parenchyma tissue ; 

 in a cornstalk, a shoot of asparagus, 

 or the trunk of a palm they are dis- 

 tributed through the whole stem. 

 As in the dicot and conifer bundles, 

 the water-conducting tissue is on 

 the side next the center of the 

 stem, and the food-conducting tis- 

 sue is on the side toward the epi- 



FiG. 78. Diagram showing the path 

 of the fibro-vascular bundles in stems 

 of the pahn type. The bundles of 

 each leaf arise by the growth outward 

 of the innermost and largest bundles 

 of the stem at that point. Lower 

 down, these bundles connect with 

 the outer bundles of the stem. {From 

 "Plants and Their Uses," by Frederick 

 Leroy Sargent; Henry Holt &° Co.) 



