THE STEM. 47 



cambium cells. Test for lignin, and study the mode of 

 development of the wood. 1 



PHYSIOLOGY OF THE STEM. 

 Protection. 



I. Examine under a lens the stem of the cultivated 

 verbena, primrose, and other plants from the greenhouse. 



II. Mount portions of the epidermis of each in water, 

 and examine with the compound microscope. Draw and 

 describe the various epidermal appendages. 



III. Make a careful study of the protective arrange- 

 ments of the common thistle, teasel, honey locust, cactus, 

 and blackberry. Ascertain the morphological character 

 of their various protective structures. 



IV. Examine various woody stems, such as those of the 

 hickory and oak. Notice ' 



1. The thickness of the bark. 



2. How it accommodates itself to the growth of the 



tree. 



V. Enumerate any other means that you have observed 

 by which the stems of plants are protected. 



Mechanical Support. 



I. Study the arrangement of the wood elements of the 

 stem of the common elder. Compare it with a stalk 

 of wheat ; with the stem of a palm. Is the material 

 economically employed ? 



II. Make a transverse section of the stem of coleus. 

 Examine with the low power of a compound microscope. 



1 In connection with his study of the structure of stems, the student 

 should read Gray's Structural Botany, pp. 67-82. 



