70 OUTLINES OF PLANT LIFE. 



a result of injuries or normally, they are known as adventitious 

 buds. 



They arise in the same places and develop in the same way as lateral 

 roots ; that is, they are internal in origin, and, as they continue to grow, 

 burst through the cortex. The shoots so produced grow in the normal 

 manner. Very rarely the growing point of the root, casting off the root- 

 cap, becomes itself the growing point of the shoot. This alteration is 

 usually the result of artificial reversal of the position of the root, being 

 brought about in some potted plants by being turned upside down. 



EXERCISE XVI. 



Roots. — Germinate seeds of wheat, corn, white (or any) bean, pea, and 

 white mustard in clean damp pine sawdust or chopped peat moss. 



Observe the form and distribution of the root-hairs on younger parts 

 of the root. Let wheat grow for several weeks and observe on what part 

 of the roots the root-hairs are dying away. (If 73.) 



Observe arrangement and origin of branches in the roots of pea seed- 

 lings. (If IT 83, 84, fig. 55.) 



Grow wheat in soil, planting it about one inch deep. After two to 

 four weeks examine roots, washing away sand carefully. Distinguish 

 primary and secondary roots. (1[1[ 70, 77.) 



Observe roots of sweet potato, beet, or dahlia, thickened for storage. 



(IT 80.) 



Examine a smoothly cut end of a root (as thick as one's finger) of any 

 tree (maple, oak, elm, etc. ). Observe the bark ; the wood with concen- 

 tric layers (annual rings). (T[ 79.) Compare with the stem of same tree. 

 Contrast with structure of a root of lily or marsh marigold. 



Examine the root of a lily, or marsh marigold, by cutting cross^sec- 

 tions and by dissection. Observe (a) the central stele, {b) the cortex. 



86. Summary. — True roots are found only in fernworts 

 and seed plants. Primary roots are usually transient ; second- 

 ary roots may be transient or permanent. Both grow at ihe 

 tip only, which is protected by the root cap. The young parts 

 form numerous root-hairs, which are sloughed off after a short 

 time (a few days or weeks) with the outer surface. The cen- 

 tral stele is chiefly for conduction of water and foods in young 



