40 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



mass of pith composing the main bulk of the stem, and the 

 many little harder and more opaque spots, which are the 

 cut-off ends of the woody threads known as fibro-vascular 

 bundles. 



C. Split a portion of the stem Jengthwise into thin, translucent 

 slices, and notice whether the bundles seem to run straight up 

 and down its length ; sketch the entire section ( X 2). Every 

 fibro-vascnlar bundle of the stem passes outward through 

 some node in order to connect with some fibro-vascular 

 bundle of a leaf. Knowing this fact, the student would 

 expect to find the bundles bending out of a vertical position 

 more at the nodes than elsewhere. Can this be seen in the 

 stem examined? Observe the thickening at the nodes, and 

 split one of these lengthwise to show the tissue within it. 



D. Compare with the corn stem a piece of palmetto and a piece 

 of cat brier (^Smilax rotundifolia, S. hispida, etc.), and notice 

 the similarity of structure. Compare also a piece of rattan 

 and of bamboo. 



Minute structure. 



E. Stain a thin cross seetioni with phloroglucin (Sec. 12, D) and sketch with 

 m.p. one of the larger bundles (some distance in from the rind). In your 

 drawing color the stained portions, which represent the lignifled scleren- 

 ohyma fibers. Look for stained rigid tissue (sclerenchyma) in the rind. 



F. Cut several yery thin longitudinal sections from a piece of stem not more 

 than one-fourth to one-third inch long, split through the middle. Stain 

 with phloroglucin and make a drawing of the best bundle found. Note 

 the two kinds of vessels, or vessel-like trachelds, some with spiral 

 threads lining the interior, and others with transverse rings. Separate 

 rings are often seen detached from their vessels and beautifully stained 

 by the phloroglucin. 



Eefeeences. Strasburger-Hillhouse, 6; Strasburger, Noll, 

 Schenck, Karsten, 1. 



A more complicated kind of monocotyledonous stem structure 

 can be studied to advantage in the surgeons' splints cut from 

 yucca stems and sold by dealers in surgical supplies. 



1 Asparagus stem may alsojje used. 



