THE VEGETATIVE ORGANS OP PLANTS. 243 



Winter wheat examined last of April 40 1 



" " " " " May 33" 



" rye " " " April 34" 



Peas examined four weeks after sowing 44 " 



" " at the time of blossom 34 " 



Hellriegel has likewise studied the radication of barley 

 and oats, (Iloff, 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 * | 25 of an inch, but a little 

 lower the diameter diminishes to about 1 | 100 of an inch. 

 Retaining this diameter, they pass downward, dividing 

 and brandling 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 ; 1 1 40 cub. foot, (4 x 4 x 2 3 1 4 in.,) 

 answered for a barley plant ; l | 3a cub. foot for an oat plant, 

 in 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, compactor soil, a similar plant 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. 



