34 ROOTS 
representing the relative amount of the three kinds of 
tissue and their relative position. 
Both fibrous roots and tap roots may become much 
enlarged as, e. g., the dahlia, sweet potato, parsnip, car- 
rot and turnip. Why not call these underground stems? 
Make cross sections of the enlarged roots used in exp. 
22 and ascertain the cell contents as far as possible. 
Which tissue (bark, wood, or pith) has become most 
modified in the enlargement of the roots? What is the 
function of enlarged roots? ‘This question may be 
answered by the following experiments: 
Exp. 23: With iodin test cross sections of a clover 
root taken from the soil in the fall after all growth has 
ceased, and of another taken from the soil in spring, after 
it has produced a stem 20 to 4c cm. long. Results; con- 
clusions? 
Exp. 24, Class: Cut a large carrot in half crosswise, 
hollow out the cut end of the upper half, hang it in a 
warm, well-lighted place, and keep the cavity filled with 
water. Why can the carrot grow without soil? 
Root-hairs and Root-caps. 
Ask the instructor for kernels of barley, wheat, or 
oats that have germinated in a damp chamber.* Note that 
the roots contain numerous hair-like projections, root- 
hairs. In which region of the roots are they largest and 
most numerous? Are they found on all parts of the 
roots? Do you find them on roots that grow in water? 
You should be able to explain the cause of this later. 
* Roots to be used for this work can be readily grown by soaking kernels of 
wheat or oats in water twenty-four hours and then scattering them on mosquito 
bar suspended about 2 cm. above the surface of water ina damp chamber. 
