52 



BIOLOGY FOR BEGINNERS 



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FIG. 9. Root Structure. 



Figure 1. A Fleshy Root. In this diagram can be seen the general region 

 of a typical root, so enlarged by food storage as to be easily visible to the 

 naked eye. 



Note especially the ducts in the central cylinder, from which extend 

 secondary branch roots, penetrating the cortex, but not connecting with it. 

 Where they come out they make the tiny cavities characteristic of the surface 

 of a carrot or parsnip. 



See also that the stem is mainly connected with the ducts of the central 

 cylinder, and not with the cortex which is mainly an outer layer of stored food. 



Figure 2. Root Tip. Here is shown the general structure of a root tip 

 under low power magnification; these parts can be seen on any growing root 

 from germinating seed. 



Note the protective root cap, and back of that a region without root hairs 

 which includes the growing point. The root hairs, if developed here, would 

 be torn off as growth proceeded, hence begin to grow further back from the tip. 



The root hairs are infinitely numerous, and only a few are shown to indi- 

 cate their comparative length and thinness of wall, and how they develop 

 from epidermal cells. 



The central cylinder and cortex can be distinguished in such a root, es- 

 pecially if it be left in a red ink solution till the ducts have begun absorption, 

 which makes the central cylinder much darker than the cortex. 



Figure 3. The Root Tip in detail. This shows the extreme tip, much more 

 highly magnified. The separate cells show plainly, and those near the grow- 

 ing points are particularly full of protoplasm and have large nuclei, showing 

 that they are in active growth. 



The loose cells of the cap have few nuclei and are largely dead cells, thrown 

 off as protection to the delicate tip. 



The ducts begin to show as thicker rows of cells though not very tubular 

 at this stage. 



The epidermis shows plainly as a single layer of cells packed in like bricks. 



