PLANT PRODUCTS 143 



composed of cellulose which may be modified into lignin (wood 

 cells) or into suherin (cork cells), by impregnation with various 

 compounds. These various modifications which plant cells 

 undergo make the wood <w other cell wall structures useful for 

 various commercial purposes. The best grade of cellulose is 

 used in the manufacture of paper and celluloid. The suberized 

 structures in woody plants have many uses in commerce. The 

 variations of cell structures give the great varieties of woods 

 which are a study in themselves. Cotton and linen goods, ropes, 

 carpets and numerousi other manufactured products illustrate 

 the many and diverse uses of plant fibers. Among the most im- 

 portant fiber plants are cotton, fiax, heimpi, jute, manila hemp 

 and sisal. The study of vegetable drugs and drug plants is 

 another extensive line of work which can only be referred to at 

 this time. 



The value of our forests for lumber, which is used in so 

 many ways, and for fuel is very generally recognized and has 

 given rise tO' that very important part of botany known as for- 

 estry. However, it is not so' generally recognized by many 

 people that the great beds of coal have been derived from 

 ancient forms of vegetation, mostly moss plants and ferns or 

 fern-like plants. 



LA?OEATORY EXERCISES. 



Exercise 1. Examine a thin section of potato from near the center of 

 the tuber. Note the large cells, thin walls and starch grains. Add a drop 

 of weak iodine and again note the starch grains. 



Exercise 2. Examine another section cut so as to show the cells near 

 the surface. Note how these cells differ from those in the interior. Add 

 a drop of weak iodine and note the yellowish tint of the crystalloids which 

 indicates their nitrogenous character. 



Exercise 3. Repeat 1 and 2, using fleshy roots of various plants and 

 fruits of apples and other plants. Compare with 1 and 2. 



Exercise 4. Examine a section of a cotyledon of a pea. Note the starch 

 grains and compare them with those of the potato. Also note the very 

 small aleurone grains in the same cells as the starch grains. Add a drop 



