THE VEGETATIVE ORGANS OF PLANTS. 243 
Winter wheat—examined last of April......... 40, )* 
“ 3 “ ‘62 ¢¢ May Ge tne ae 99 
Sere TYC ss $6 CO OTD re cea 34S 
Peas examined four weeks after sowing........ 44 “6 
He us at the time of blossom......... 24 
Hellriegel has likewise studied the radication of barley 
and oats, (Moff, Jahresbericht, 1864, p. 106.) He raised 
plants in large glass pots, and separated their roots from 
the soil by careful washing with water. He observed that 
directly from the base of the stem 20 to 30 roots branch 
off sideways and downward. ‘These roots, at their point 
of issue, have a diameter of *|,, of an inch, but a little 
lower the diameter diminishes to about *|,,, of an inch. 
Retaining this diameter, they pass downward, dividing 
and branching to a certain depth. From these main roots 
branch out innumerable side roots, which branch again, 
and so on, filling every crevice and pore of the soil. 
To ascertain the total length of root, Hellriegel weighed 
and ascertained the length of selected average portions. 
Weighing then the entire root-system, he calculated the 
entire length. He estimated the length of the roots of a 
vigorous barley plant at 128 feet, that of an oat plant at 
150 feet.* He found that a small bulk of good fine soil 
sufficed for this development ; *|,, cub. foot, (4 4 x 2°|, in.,) 
answered for a barley plant; *|,, cub. foot for an oat plant, 
im these experiments. _ 
Hellriegel observed also that the quality of the soil in- 
fluenced the development. In rich, porous, garden-soil, a 
barley plant produced 128 feet of roots, but in a coarse- 
grained, compacter soil, a similar p'ant had but 80 feet of 
roots. 
Root-Hairs,—The real absorbent surface of roots is, in 
most cases, not to be appreciated without microscopic aid. 
The roots of the onion and of many other bulbs, i. e., the 
fibers which issue from the base of the bulbs, are perfectly 
* Rhenish feet 
