AN INTRODUCTION TO PLANT BIOLOGY 



69 



FIG. 25. Root- 

 tubercles. 



In addition to the structures already noted, there are 

 on the roots many delicate root-hairs (Fig. 26). Their great 

 importance in absorbing water will be explained later. 

 They are usually so firmly attached to soil par- 

 ticles that they are broken when the plant is 

 lifted from the soil. It is well known to gar- 

 deners that it is easy to transplant many plants 

 if one carefully lifts a mass of soil so as not to 

 disturb that near the roots and thus break the 

 delicate root-hairs. 



(L) Examine a bean root and note that a layer of 

 rind or bark (cortex, or cortical layer) is easily scraped 

 or stripped from the central cylinder of wood. Test 

 the strength of this central cylinder of a small root by 

 pulling and by bending. How are strong roots of 

 advantage to the plant? Tear a root lengthwise and note the 

 fibers which make it strong. 



68. Microscopic Examination of Roots. (D) Mount on an 

 object-slide, with cover-glass, some small roots from Tradescantia 



stems kept in water, or from 

 seedlings of bean, radish, clover, 

 oats, or barley, grown on moist 

 blotting-paper ( 81). Using 

 first the low power, note (1) a 

 cap-like structure on the tip of 

 the root (Fig. 27), (2) a some- 

 what opaque central cylinder, 



(3) a transparent rind outside, 



(4) the outermost layer of the 

 rind is the very transparent 

 epidermis. 



FIG. 26. Cross section of root, showing Cells. Now, using the high 



central woody cylinder; rind or cortex; power of the microscope, notice 



root-hairs with particles of adhering ^^ the rQot ig composed o f 



sod. (After Frank.) ^.^ structureg> the cdls 



(Pig. 27). Are they all the same shape ? Many of the cells contain 

 living matter (protoplasm), but some appear empty. (D) If some 

 iodine-eosin (eosin dissolved in a solution of iodine) be drawn under 

 the cover-glass by means of absorbing-paper touched to the edge of 

 the glass opposite a drop of the stain, the protoplasm in the cells will 



