THE ROOT— FUNCTION AND STRUCTURE 



47 



Fig. si.— 

 Plant grow- 

 ing IN In- 

 verted Pot. 



or weeks, note that the bulb has been raised out of the earth by 

 the forming roots. All roots exert pressure on the soil as they grow. 

 Explain. 30. Response of roots and stems to the force of gravity, 

 or geotropism. Plant a fast-growing seedling in a 

 pot so that the plumule extends through the drain 

 hole and suspend the pot with mouth up {i.e. in 

 the usual position). Or use a pot in which a plant 

 is already growfng, cover with cloth or wire gauze 

 to prevent the soil from falling, and suspend the 

 pot in an inverted position (Fig. 51). Notice the 

 behavior of the stem, and after a few days remove 

 the soil and observe the position of the root. 31. If 

 a pot is laid on one side, and changed every two 

 days and laid on its opposite side, the effect on the 

 root and stem will be interesting. 32. If a fleshy 

 root is planted wrong end up, what is the result ? 

 Try it with pieces of horse-radish root. 33. By 

 planting radishes on a slowly revolving wheel the 

 effect of gravity may be neutralized. 34. Region of 

 root most sensitive to gravity. Lay on its side a pot containing a 

 growing plant. After it has grown a few days, wash away the earth 

 surrounding the roots. Which turned downward most decidedly, 

 the tip of root or the upper part? 35. Soil texture. Carefully turn 

 up soil in a rich garden or field so that you have unbroken lumps 

 as large as a hen's egg. Then break these lumps apart carefully 



with the fingers and 

 determine whether 

 there are any traces 

 or remains of roots 

 (Fig. 52). Are there 

 any pores, holes, or 

 channels made by 

 roots ? Are the roots 

 in them still living ? 

 36. Compare an- 

 other lump from a 

 clay bank or pile 

 where no plants 

 have been growing. 

 Is there any differ- 

 ence in texture? 37. Grind up this clay lump very fine, put it in 

 a saucer, cover with water, and set in the sun. After a time it 

 will have the appearance shown in the lower saucer in Fig. 43. 

 Compare this with mellow garden soil. In which will plants grow 

 best, even if the plant-food were the same in both ? Why? 38. To 

 test the effect of moisture on the plant, let a plant in a pot or box dry 



Fig. 52. — Holes in Soil made by Roots, now 

 decayed. Somewhat magnified. 



