58 



STRUCTURE OF THE STEM 



FIG. 64. Diagrammatic cross section 

 of stem of Indian corn 



cv, fibro- vascular bundles; gc, pithy 

 material between bundles. After 

 Strasburger 



In the bamboo, as in the cane 

 of our southern canebrakes, the 

 interior is hollow, with a hard, 

 transverse partition at each 

 node. 



The fibers which traverse the 

 pith of the corn stem are not 

 solid cylinders, but are built 

 up of cells of several kinds, 

 around and between tubes, 

 somewhat like those of Fig. 62. 

 The whole structure is known 

 as afibro-vascular bundle; that 

 is, a bundle of fibers and ves- 

 sels, or tubes. In woody stems, 

 such as those of the bamboo 

 or palm, the bundles are closer 



together and much harder than in the corn stem. The outer 



rind of the latter is composed of long, thick-walled, slender 



cells, containing much silica and known as sclerenchyma fibers. 

 72. Mechanical function of the manner 



of distribution of material in monocoty- 



ledonous stems. The well-known strength 



and lightness of the straw of our smaller 



grains and of rods of cane or bamboo are 



due to their form. It can readily be shown 



by experiment that an iron or steel tube of 



moderate thickness, like a piece of gas pipe 



or of bicycle tubing, is much stiffer than a 



solid rod of the same weight per foot. The 



oat straw, the stems of bulrushes, the cane 



of our southern canebrakes, and the bam- 

 boo are hollow cylinders ; the cornstalk is 



a solid cylinder, but filled with a very light pith. The flinty outer 



layer of the stalk, together with the closely packed sclerenchyma 



FIG. 55. Diagrammatic 

 cross section of stem 

 of bulrush (Scirpus), a 

 hollow cylinder with 

 strengthening fibers 

 After Kerner 



