VII. ROOTS AND THEIR WORK 



The development of a bean seedling has shown us that the root 

 invariably grows first. One of the most important functions of the root 



to a young plant is that of a holdfast, an anchor to 

 fasten it in the place where it is to develop. This 

 chapter will show us very many other uses of 

 the root to the plant, the taking in of water, 

 the storage of food, climbing, etc. All other 

 functions than the first one stated arise after 

 the young plant has begun to develop. 



Root System} — If you dig up a young bean seed- 

 ling and carefully wash off the roots, you will see that 

 a long root is developed as a continuation of the hypo- 

 cotyl. This root is called the primary root. Other 

 smaller roots which grow from the primary root are 

 called secondary, or tertiary, depending on their relation 

 to the first root developed. In a young plant, notice 

 the general direction taken by the roots. Can you give 

 any reason for the spreading out of the roots in all 

 directions ? 



Make a drawing of the root system of a seedling; 

 label all its parts. 



Young bean plant, 

 showing primary 

 and secondary 

 roots. 



Downward Growth of Root. — Most of the roots examined take 

 a more or less downward direction. We have already seen that 

 factors outside of the seed call it into activity and cause what we 

 call germination. Might external factors cause the root to grow 

 downward, and if so, what are the factors? 



The following apparatus and experiments will throw some light 

 on this question. 



The Pocket Garden} — A very convenient form of pocket germinator 

 may be made in a few minutes in the following manner: Obtain two 

 cleaned four by five negatives (window glass will do) ; place one fiat on the 

 table and place on the glass half a dozen pieces of colored blotting paper 

 cut to a size a little less than the glass. Now cut four thin strips of wood so 

 as to fit on the glass just outside of the paper. Next moisten the blotter, 



* See Hunter and Valentine, Mantud, page 20. 



82 



2 Ibid., page 233. 



