12 REPRESENTATIVE PLANTS 



observe the outer cells (epidermis) ; the central axis {stele); 

 the cell layers between these two (cortex). 



Draw these features of a root (I})). 



Root hairs, their use. Read about the subject of " Hoot 

 Hairs" and find the purpose of the hairs. By what pro- 

 cess do they accomplish this purpose ? Estimate, if you 

 can, how much they increase the root surface. What effect 

 would the " pulling up " of a seedling have on these frail 

 structures ? How then should plants, in transplanting, 

 be treated ? What damage would be caused by dry air ? 



2. The Purpose of Roots 



Uses. Roots have one or more of the following uses : 

 (1) As holdfasts ; (2) as absorbers of moisture and food 

 material in solution ; (3) as storehouses of reserve food. 



Their forms are, therefore, variously modified to meet 

 these demands made upon them. Roots are, furthermore, 

 markedly influenced by soil conditions, resulting in well- 

 marked peculiarities of shape and extent. 



Forms. Tlie primary tap root. When the radicle end of 

 the hypocotyl develops a single root, whose direction of 

 growth is directly downward, the branches being much 

 smaller and short, such a root is a tap root. Examine the 

 roots of corn, pea, spinach, and any other forms furnished, 

 and determine which answer the requirements of the tap 

 root. Many such roots have naturally, or by cultivation, 

 become very fleshy with reserve food and then are called 

 storage roots. Examine the roots of carrots, parsnips, tur- 

 nips, beets, salsify, horse-radish, and radish. 



Draw the various forms of tap roots you have on hand, 

 naming such as are storage. 



Examine, at this time, the roots of the onion and observe 

 that, while they are multiple primary roots, each root itself 

 is not fleshy but threadlike or fibrous. Examine grass roots, 

 oats, wheat, and other forms showing fibrous character. 



