THE IMPORTANCE OF THE ROOT-SYSTEM 151 



in Fig. 12 this covering is present all over the root, with the exception of 

 the extreme apex where no root-hairs are present, whereas in the older 

 root-system of Triticum shown in Fig. 13 the soil remains attached only 

 to the younger parts to which root-hairs are now restricted. 



From the above it is clear why plants wither much sooner when only the older 

 parts are submerged, than when the younger parts are in contact with water. This 

 was first observed by de la Baisse l , who passed the younger roots through the tube 



FIG. ii. A, rhizoidof Polytrichumjuniperinum\ B, of Marchantia 

 polymorpha (X24o\ C, root-hair of Poa annua; and D of Draba 

 verna (X32o). The preparations are obtained by shaking gently in 



FIG. 12. Seedlings of Sinapis 

 alba grown in sand. A has been 

 gently shaken to remove the 

 superfluous sand particles. In 

 B, the sand particles have been 

 removed by gentle agitation in 

 water. (After Sachs!) 



of a filter-funnel, and closed the mouth of the tube, so that, on filling the funnel, 

 only the older roots were in contact with water. By means of aniline dyes capable 

 of absorption, it may be shown that, even after several days, no perceptible 

 amount penetrates the older parts of the root, whereas in the younger parts, the 



aldehyde has been added, permanent preparations suitable for demonstration may be made. For 

 such purposes it is best to use roots grown in emery powder. 



i De la Baisse, in Duhamel, Naturgesch. d. Baume, 1765, Bd. II, p. 148. Similar researches on 

 horse-radish roots are given by Senebier (Physiol. veget., 1800, T. I, p. 3") and by Meyea 

 (Physiol., 1838, Bd. II, p. 18). 



