124 ROOTS 



The work of plants is subdivided, but it is also united. 

 So our study must be subdivided, but also united. You 

 will read chapters on roots, stems, and leaves separately, 

 but you will think of- them together. You will have your 

 facts classified into topics. You will also understand their 

 relationship to each other. You will perceive their unity 

 as well as their separateness. 



41. Introductory as to Roots. — You already know a 

 good many important things about roots. You know that 

 they are the burrowing parts of plants ; that they seem 

 to be seeking in the soil for things -the plant needs. You 

 know that they anchor the plant ; that their extent may be 

 even greater than the extent of the stem and its branches. 

 You know that they seem to respond to the nature of the 

 soil in which they grow, suiting their structure to the con- 

 ditions they meet. You know that there is a dense growth 

 of delicate hairs just back of the growing tips, and that 

 these hairs are organs of absorption. You know that a 

 great deal of water is absorbed by roots, though it is only 

 through the tips of young roots and through root-hairs 

 that this water enters. You know that, in the water of 

 the soil, substances which the plant uses in food manu- 

 facture exist as solutes, and that by osmosis these solutes 

 enter the roots. You know that the internal structure of 

 all roots is quite similar, and have noted the relationship 

 and appearance of epidermis, cortex, and stele. You know 

 that the absorbed substances pass through the cortex, reach 

 the stele, and move through the xylem up toward the stem, 

 while through the phloem food descends from above. You 

 know that food is often stored up in the roots, and that 

 the roots of some plants live throtigh the winter, while the 



