STEMS 99 



height in proportion to tliickness, and show greater 

 strength and efficiency, than those built by man. 



129. Arrangement of mechanical tissues iti a 

 stem of a grass. — Secure an uninjured cornstalk. 

 Take out a single internode, or the part between 

 two joints, and dissect it. Note the hard plates 

 which extend entirely through the stem at the nodes. 

 The outer layer is in the form of a cylinder and is 

 hard and rigid. Cut in two parts lengthwise. The 

 interior is filled with the soft pith. In this pith 

 are great numbers of strands and fibres which run 

 from the plate at one end to the other. Now split 

 the entire piece into small strips, and without injur- 

 ing any of the separate parts tie them together in 

 a bundle. Lay the bundle on a table with half of 

 its length projecting over the edge. Weight down 

 the end on the table. Now tie weights to the other 

 end and determine the amount necessary to break 

 the bundle of building material. Repeat the opera- 

 tion with a section of the stem which has not been 

 dissected. It will doubtless be seen that the mate- 

 rials themselves are not very strong, but when fitted 

 together in proper form they make an extremely 

 rigid stem. 



