THE STEM. 5 



wheat i)lant still older than the one shown in the previous figure. 

 Here the root-tips are naked and the older roots fail to retain the 

 particles of soil because the hairs have perished. It will be seen 

 that the root-hairs are confined to the younger portions of the 

 roots, beginning a little back from the tip. 



These hairs look somewhat like mould or a mass of spider's 

 webs and can be easily seen where Indian corn or Avheat is sprouted 

 between folds of damp cloth or paper. They are the chief 

 agents for absorbing water and gases from the soil. 



Root-hairs not only take up substances held in solution, but 

 through their acid act on solid substances and render them soluble. 



They also obtain nitrogen in the form of nitrates, which to some 

 •extent are formed in the soil through the action of bacteria, the 

 lowest and simplest and smallest of plants. 



The root-hairs nearly or quite all perish when a plant is at rest 

 or ceases to grow, but when growth begins again it sends out new 

 rootlets which produce new root-hairs. 



Trichomes are usually found to a greater or less extent on 

 stems, leaves, and even on some parts of the flower. 



The Stem. The ascending axis or stem of a grass is called the 

 culm. Some grasses produce stems on the surface of the ground or 

 beneath it; these are called rhizomes oy root-stocks. They often 

 bear roots and sheathing scales, or rudimentary leaves with good 

 buds, as is seen in June grass and quack grass. 



The full grown culms of nearly all grasses are hollow, with solid 

 or knotted joints called riodes. When very young the internodes 

 or spaces between the nodes are solid, and even when full grown 

 they are solid in most root-stocks, and in the culms above ground 

 of such grasses as Indian corn, broom corn, sorghum, and sugar- 

 cane. In case of Phleum pratcnse (Timothy), Poa hidhosa, 

 Arrhenaflierum avenaceum (tall oat grass), some of the lower 

 short internodes become enlarged and contain a store of nourish- 



