TYPES OF ROOT SYSTEMS 



139 



their numerous fine branches form a system resembhng a fine 

 brush when the dirt is washed away. {Fig. 122.) This type of 

 root system is common among weeds, trees, and 

 many cultivated plants. In addition to the un- 

 derground roots, some of the Grasses, as Corn- 

 illustrates, develop -prop or Irace roots, which 

 grow out from nodes above the ground into 

 which they finally reach to afford additional an- 

 chorage. However, brace roots are not neces- 

 sarily an accompaniment 

 of fibrous root systems, 

 for they may occur in 

 connection with other 

 kinds of root systems. 



The tap-root system, in 

 which there is one large 

 main root from which 

 smaU lateral branches 

 arise, is typical of the 

 Alfalfa, Red Clover, 

 Beets, Dandelion, and 

 numerous other plants. 

 Tap-roots usually grow 

 directly downward, pen- 

 etrating into the deeper 

 layers of the soil where 

 more moisture is avail- 

 able. {Fig. 123.) For 

 this reason, the tap-root 

 system is best adapted for dry regions 

 and is, therefore, characteristic of drought 

 resistant plants. Although the tap-root 

 is more common among herbaceous 

 plants, it occurs, nevertheless, among 

 trees, where it often interferes with trans- 

 planting, as in case of Hickories, Oaks, 

 and Maples. {Fig. 124.) 



Tap-roots are also convenient storage 

 organs in which food is stored for the growth of the new shoot 

 the next year. This fact is well illustrated in Alfalfa, Clover, 



Fig. 123. — 

 Alfalfa, a plant 

 with a promi- 

 nent tap-root. 



Fig. 124.— Young SheU- 

 bark Hickory, showing the 

 tap-root. After Farmers' 

 Bulletin 173, U. S. Dept. 

 of Agriculture. 



