Ch. V, 3] ANATOMY OF ROOTS 221 



A very thin section cut longitudinally through the tip 

 of an ordinary root, e.g. of Corn, presents under the micro- 

 scope the aspect here pictured (Fig. 162). Close to the coni- 

 cal end stands out the growing point, distinguished by its 

 many small, densely-packed cells, which are squarish in 

 section, thin-walled, and filled with the all-important 

 protoplasm. This is the place of cell-formation for the en- 

 tire tip of the root, the new cells being made by division 

 from a small central group, after which they absorb nourish- 

 ment and enlarge to the original size. In front these new 

 cells are constantly forming the root cap, becoming larger 

 and empty near the outside, where they are continuously 

 abraded away by the forcible passage of the root through the 

 soil. Backwards, in the growth zone, the cells hold the reg- 

 ular ranking in which they are formed, but grow rapidly 

 larger, especially in length, while keeping their thin walls, 

 to which the protoplasm comes soon to form only a lining. 

 Each individual cell, in fact, immediately after its formation, 

 goes through a grand period of enlargement (page 156), soon 

 reaching its maximum size; and this explains how the 

 growth zone follows so closely behind the growing point. 

 Here also can be seen the beginning of the cellular differentia- 

 tion of the fibro-vascular bundles, while the intercellular 

 aeration system also is plain, though it does not appear in 

 our drawing. Backward the growth zone merges impercep- 

 tibly into the hair zone. The hairs originate as slight swellings 

 from the outer walls, and grow rapidly longer until they 

 attain the familiar tube form. In this zone appear also the 

 striking fine spirals of the ducts, of which the mode of for- 

 mation is clearly apparent in good sections. The end walls 

 in a long line of superposed cylindrical cells break down, 

 under action of digestive enzymes, while simultaneously 

 the spirals begin to appear as local thickenings of the 

 walls. 



These sections show further that the outermost layer 

 of cells of the root possesses no breaks or openings of any 



