38 STUDY OF COMMON PLANTS. 



IV. THE STEM. 



MATERIAL EEQUIEBD. 



Fresh shoots of apple-tree, grape-vine, oak, elder, and basswood. 

 Stalks of Indian corn put up in alcohol after they have attained full 



size. Stems of common greenbrier, Smilax rotundifolia, L. 

 Shoots of white pine from one to three years old, preserved in alcohol. 



Similar specimens of arbor vitas or of red cedar. 

 Specimens of white oak, hickory, ash, Norway spruce, palm, and other 



woods, showing transverse and longitudinal sections. 

 A collection of greenhouse plants, including rose geranium, primrose, 



Coleus, Tradescantia, and others. 

 Tendrils of grape-vine, spines of honey locust, common potato, and 



such other modified stems as are procurable. 



STRUCTURE AND MODE OF GROAVTH. 



I. Study first the gross anatomy of a number of woody 

 stems. 



1. Witli a sharp knife make a transverse section of a 



one-year-old shoot of an apple-tree. Examine 

 under a good lens, and draw an enlarged outline, 

 showing the position and relative proportions of 

 pith, wood, and bark. 



2. Separate the bark into its three layers, 

 a. External, corky layer. 



I. Middle, green layer, not sharply delimited from the 

 c. Inner bark, or bast. 



Try the strength of these different parts by sepa- 

 rating and pulling upon them. 



