THE RADICLE AND THE ROOT. 



33 



Fig. 30. —Root-hairs or Absorptive Cells of Pen- 

 stemou with adherent particles of earth. 



In this condition they are not unlike the minute 

 threads of a fungus, but the hairs are shorter, 

 straighter, and 

 not so much in- 

 terwoven. 



The extreme 

 tip of the pri- 

 mary root gen- 

 erally looks a 

 little thickened; 

 and if it be 

 examined with 

 a magnifying- 

 glass, a little 

 thimble- shaped 



sheath may be observed covering the end of 

 the root. This is the root-cap (fig. 31). It may be 

 seen with an ordinary pocket magnifying-glass 

 in the roots of duckweed (Lemna), and by the 

 aid of the microscope in almost all roots in 

 their young state. The root-cap acts as a pro- 

 tection to the young growing-point of the root. 

 As the direction of growth of the root is from 

 above downwards, it is obvious that the roots, 

 by reason of the screw-like movement before 

 mentioned, insert themselves between the par- 

 ticles of the soil, 

 and in so doing 

 would be likely to 

 injure the delicate 

 young cells at the 

 tip were it not 

 protected by the 

 root-cap. Already 

 then, in this early 

 stage of the root, 

 we find variations 

 in structure; we find root-hairs and we find a 

 root-cap both produced from the outer portion 

 of the root, the one alive and active, the other 

 dead but protective. The main portion of the 

 root is occupied externally by cells only, which 

 constitute the cortex or rind, whilst the extreme 

 centre is occupied by a strand of cells which 

 have lost their original more or less globular 

 form, and have lengthened into vessels and 

 tubes of various kinds. 



Root Action. — The root is now complete as to 

 essentials, and is fully equipped for work. What 

 is that work 1 ? Briefly, it is the absorption of 

 water and air from the interstices between the 

 particles of soil, and from the film which covers 

 each particle. That water contains, in solution, 

 some of the food which is required by the plant. 

 We say some, because there is much that is not 

 soluble in water, and so the plant might starve 

 Vol. L 



Fig. 31 —Section through the Root-tip of 

 Penstemon. The bowl-shaped mass at 

 the tip is the root-cap ; X 60. 



in the midst of plenty were it not for two cir- 

 cumstances that enable it to avail itself of matters 

 that are usually insoluble. One is the presence 

 of the right kind of microbe, or bacterium, to 

 convert the insoluble into the soluble; the other 

 is a property with which the protoplasm of the 

 roots themselves is more or less endowed, that 

 of secreting a solvent juice which, coming into 

 contact with certain elements of the soil, effects, 

 with the addition of water, the dissolution of 

 some of the earthy or mineral matters of the 

 soil, and renders them available for absorption 

 by the plant. 



But it is not only liquid food, or liquids out 

 of which food can be manufactured, that enter 

 the plant by means of the fine extremities of 

 the roots, and by the root-hairs in particular; 

 gases are also absorbed, and in particular oxygen 

 gas. This statement can only be proved in the 

 laboratory, but the ill effects consequent on 

 excluding the air from the roots are familiar to 

 gardeners in the case of trees that have been 

 planted too deeply, or whose young feeding 

 roots are buried beneath an impermeable coat- 

 ing of asphalte, or even soil so trodden down 

 or so stiff as not to allow of the penetration of 

 the air. 



So far we have been assuming the existence 

 of a single root-fibre, as in a seedling plant of 

 mustard, but in most cases the root does not 

 remain in this simple condition ; it branches and 

 branches asjain till often a dense network of 



Fig. 32.— Meadow Grass- 

 Fibrous Root. 



Fig. 33.— Dahlia— Tuberous 

 Root. 



so-called fibrous roots is formed, as in the case of 

 grasses (fig. 32). These branches, unlike the root- 

 hairs which spring from the surface, only emerge 

 from the central portions of the root and make 

 their way outwards. In other instances the 

 original body of the root remains, increases in 

 size and thickens in texture, so that we get 

 what are termed tap-roots. Sometimes, as in the 



3 



