THE ROOTS 27 



26. Shrinkage of roots to aid in fixation. — Ex- 

 amine the full-grown roots of a hyacinth {Hya- 

 cinthus), calla, or jack-in-the-pulpit (Arismma). A 

 short distance back of the tip the surface appears to 

 be wrinkled. The wrinkling is due to the fact that 

 the root elongates by growth at the tip, and as soon 

 as any portion reaches a certain age, it shortens and 

 causes little folds to appear on the surface tissue, or 

 epidermis. If India-ink marks are placed on young 

 roots, and the distance between them measured be- 

 fore and after wrinkling, it will be found that some 

 shrink one-tenth or even one-fifth of their whole 

 length. If the shrinkage of the root simply pulled 

 it through the soil, it could be of no benefit to the 

 plant and might work damage. The tip of the root, 

 however, is firmly attached by means of the root- 

 hairs, and then this portion is bent around so many 

 small rocks that it is not easily pulled back by the 

 contraction. As a result, the base or upper end of 

 the root with the stem to which it is attached is 

 pulled down into the soil still more firmly. Further- 

 more, if the root has sent out side branches, the soil 

 between the side branches will be clamped between 

 them in a manner well illustrated by the masses of 

 rock and dirt seen adhering to the roots of pros- 



