THE ROLE OF GREEN PLANTS 



243 



The Root and Its Work 



Recent experiments made by Weaver ^ and others show that plants 

 have extremely comphcated root systems. The roots of an old oat 

 plant, for example, although extending through only about two cubic 

 yards of soil, were found to have a total length of over 450 feet. 

 Weaver found that hardy wheat plants sent their rootlets into the 

 soil six feet below the surface 



^,CeJ7tml Cylinder- 

 -_>v&ocf^ bundle 



-root "hciiT~ 



ictermis 



of the ground. In the bush 

 morning-glory, a common 

 plant of the mid-western 

 plains, the roots may extend 

 ten feet into the ground and a 

 distance of twenty-five feet 

 away from the parent plant. 

 The roots of corn extend 

 laterally three to four feet 

 from the stem and sometimes 

 over seven feet into the soil. 

 All this is evidence for the 

 great importance of the root 

 as an absorbing organ. 



Examination of longitudinal 

 sections cut from growing 

 roots shows that the body of 

 a root is made up of a central 

 woody cylinder surrounded 

 by layers of softer cells, collec- 

 tively called the cortex. Over 

 the lower end of the root is 

 found a collection of cells, 

 most of which are dead, ar- 

 ranged in the form of a cap 



covering the growing tip. As the root pushes through the soil, the 

 outer cells of this root cap are sloughed off, and are rapidly replaced 

 by growing cells of meristem that are just under the root cap. The 

 root cap proper is evidently a protective adaptation. In the woody 

 region of the root are vascular tissues consisting of xijlc77i and phloem. 

 These tissues form a series of tubelike structures which together with 



. >■-' J~OOt/ 



cctp 



Root of a dicotyledon, greatly magnified. 

 Find the functions of each part labeled. 

 How might soil water get from the outside 

 of the plant into the woody bundles.'* 



' Weaver, Root Development of Field Crops, McGraw-Hill Book Co. 



