168 



APPLIED BIOLOGY 



.FiG. 44. Transverse section 

 of corn stem showing rind 

 (r) , pith (p) , and numerous 

 fibro-vascular bundles (v). 



does occur, as in some palms, is due to expansion of the 

 first-formed cells, not to new layers of cells added between the 

 bark and wood, as in the dicotyledons 



( 162). 



Structure of Corn Stalk. (L) Cut a 

 dry corn stalk (stem) transversely. Note 

 the smooth rind (not true bark) on the out- 

 side, and inside the rind is the soft pith 

 throughout which the fibro-vascular bun- 

 dles are scattered irregularly. Where are 

 the bundles largest ? Where are they most 

 abundant ? Suggest a reason for such ar- 

 rangement. 



Split a stalk lengthwise, and the fibro- 

 vascular bundles appear as long threads 

 which are easily pulled out. Trace these 

 long threads through nodes. Do they all 



continue upward or do some of them turn toward the rind at the 



nodes ? Try to trace some of the 



bundles out into the bases of 



leaves left on the nodes. 



Stand a piece of green corn- 

 stem for a short time in red ink, 



and then cut both transversely 



and longitudinally in several 



places, and find out where the 



colored liquid ascends the stem. 

 Examine with a microscope a 



thin cross section cut from a 



green stem or from one preserved 



in alcohol or formalin solution. 



Observe that all parts of the 



section are composed of cells, 



most of which are thin-walled 



pith-cells. Scattered irregularly 



among these are denser areas of 



cells, the fibro-vascular bundles. FlG - 45 - Transverse section of a 



Notice that the bundles are very S^* ^"2 



small and closely packed near a> d> sp> ducts or woo d-tubes ; str, 



the margin, thus making the firm strengthening fibers ; /, sieve-tubes ; 



rind, while the bundles toward wp, woody pith. (From Osterhout.) 



