DICCTYLEDONOUS 25 
low stem about 1.5 cm. in diameter and 15 cm. long into 
a 2 liter can containing water 2 cm. deep. Carefully 
take a ring of bark 8 mm. wide from one stem so 
that the lower edge of the ring will be 5 mm. above the 
water. See that this stem and one of the remaining are 
right side up and the third upside down. Cover the can 
and put it in a warm place (23 degrees C.) Roots will 
develop on these stems. How long does it take them 
to start? Where do they come out with reference to 
the leaf-scars? With reference to the region from which 
the bark has been removed? After having learned all 
you can about this experiment have the instructor ex- 
plain its meaning. 
Histology of Dicotyledonous Stems. 
As soon as you have finished the following study of 
the histology of the dicotyledonous stem, describe the 
ells cf each kind of tissue with regard to form as solids, 
color,-relative thickness of cell-walls, character of cells 
and contents, and also, judging from the structure of the 
cells and their contents in each kind of tissue, give the 
function of each. 
With a sharp razor cut very smal! thin cross sec- 
tions from a beech twig one year old. Mount them in 
water and study them under low power. Identify the 
bark (brown and green), wood layers and medullary rays, 
and pith. Find a very thin place near the edge of a sec- 
tion and study it under the high power. Note that the 
cavities of the cells in the brown bark are filled with 
brown substance. Draw four or five adjoining cells. 
Arrange your drawings of the cross sections so that there 
