Commercial Gardening 



the root cap, which is intended to protect the tender growing point as it 

 pushes its way amongst the particles of soil. The nature of a young root 

 may readily be seen by filling a punnet with light sandy soil and scatter- 

 ing some Mustard seed thinly over the top. Stand it in a warm, moist, 

 shady place for a few days till the seed germinates, and 

 then in a well-lighted position. From the sides of the 

 radicle numerous hairs arise, enter the soil in a horizontal 



direction, and place themselves 

 in close contact with the par- 

 ticles of soil (figs. 13, 14, 15). 

 These are the root hairs, and 

 their function is to absorb 

 water containing food in solu- 

 tion. The interstices or spaces 

 between the particles of soil 

 are filled with air, or should be, 

 for land plants, but the par- 

 ticles themselves are covered 

 with a thin film of water, and this is all that the root hairs can absorb. 

 If the interspaces are filled with water, the soil is water-logged and the 

 radicle and root hairs cannot breathe, but soon get asphyxiated and perish. 

 The radicle does not absorb water at the tip but some way behind it, and 

 only while the outer walls remain quite thin. The root hairs continue 



their work for a few days or 

 weeks, then die away and 

 leave no trace behind; but as 

 the radicle lengthens and sec- 

 ondary roots are formed, new 

 ,^ % root hairs are continually 



Fig. 12. Section through the Root 

 Tip of Pentstemon. The bowl-shaped 

 mass at the tip is the root cap; x 60. 



Fig. 13. 1, Seedling 

 with the long absorp- 

 tive cells of its root 

 (" Boot Hairs ") with 

 sand attached. 2, The 

 same seedling: the sand 

 removed by washing 



Fig. 14. Koot Tip of Pentstemon with Root Hairs penetrating 

 between the particles of soil ; xlO 



fig. 15. Root Hairs or Absorptive 

 Cells of Pentstemon with adherent par- 

 ticles of earth 



being produced, thus tapping fresh areas for food. In Dicotyledons 

 generally the primary root is permanent, and, if undisturbed, may attain 

 a great size and age in forest trees. From an early stage of growth it 

 commences to give off secondary roots which branch repeatedly, permeating 

 the soil in every direction with their finer ramifications or root fibres. In 



