THE ROOT OF THE MATTER. 



surface centrally towards the root. This is 

 the centripetal type. Such plants resemble 

 rather a funnel than an umbrella. They 

 have always a straight tap-root, like a 

 carrot ; and this tap-root gives off numerous 

 short rootlets on every side, which absorb 

 all the water as it trickles down along the 

 tapering surface of the inverted cone. The 

 other plan the centrifugal type is adopted 

 by certain plants with heart-shaped or arrow- 

 shaped leaves, which have round leaf-stalks. 

 In these cases the individual leaves point 

 outward and downward, and the water drips 

 from them not inward towards the centre, 

 but outward towards the circumference. 

 Their principle is rather umbrella-like than 

 funnel-like. To meet this catchment system 

 they have no long and descending tap-root, 

 but just a short knobby root, which gives 

 off long fibres radially in every direction ; 

 and these fibres terminate in knots or groups 

 of absorbent rootlets exactly beneath the 

 points where each leaf drips the knobs or 

 197 



