THE ROOT 



61 



Practical Questions 



1. Could any normal plant grow in a soil from which nitrogen was lack- 

 ing? Potash? Lime? Phosphorus? (62.) 



2. Could it live in an atmosphere devoid of oxygen ? Nitrogen ? Car- 

 bon dioxide? (62.) 



3. Why are cow peas or other legumes planted on worn-out soil to renew 

 it? (63.) 



4. Is the same kind of fertilizer equally good for all kinds of soil ? For 

 all kinds of plants ? (60, 62.) 



5. Why does too much watering interfere with the nourishment of 

 plants? (Exps. 26, 27.) 



6. Are ashes fit for fertilizers after being leached for lye? (62.) 



7. Why will plants die, or make very slow growth, in pots, unless the 

 soil is renewed occasionally? (60, 62.) 



III. STRUCTURE OF THE ROOT 



Material. — Taproot of a young woody plant not over one or two 

 years old ; apple and cherry shoots make good specimens. For showing 

 root hairs, seedUngs of radish, turnip, or oat are good, also roots of wan- 

 dering Jew grown in water ; for the rootcap, corn, sunflower, squash. 



64. Gross anatomy of the root. — Cut a cross section of 

 any woody taproot, about halfway between the tip and the 

 ground level, examine it with a lens, and sketch. Label 

 the dark outer covering, epidermis, the soft layer just within 

 that, cortex, the hard, woody axis 

 that you find in the center, vas- 

 cular cylinder, and the fine sil- 

 very lines that radiate from the 

 center to the cortex, medullary 

 rays (in a very young root these 

 will not appear) . Cut a section 

 through a root that has stood in 

 coloring fluid for about three 

 hours and note the parts colored 

 by the fluid. What portion of 

 the root, would you judge from 

 this, acts as a conductor of the 

 water absorbed from the ground? 



Fig. 76. — Cross section of a young 

 taproot ; a, a, root hairs ; h, epider- 

 mis ; c, cortical layer ; d, fibrovascular 

 cylinder. Note the absence of med- 

 ullary rays during the first year 0/ 

 growth. 



