382 HOW CROPS GllOW. 



root-cells into the water of the soil. This is, however, 

 no physiological action, but a purely physical process. 



Vitality of Roots. — It appears that in case of most 

 plants the roots cannot long continue their vitality if 

 their connection with the leaves be interrupted, unless, 

 indeed, they be kept at a winter temperature. Hence 

 weeds. may be effectually destroyed by cutting down 

 their tops; although, in many <;ases, the process must 

 be several times repeated before the result is attained. 



The roots of our root-crops, properly so-called, viz., 

 beets, turnips, carrots, and parsnips, when harvested in 

 autumn, contain the elements of a second year's growth 

 of stem, etc., in the form of a bud at the crown of the 

 root. ■ If the crown be cut away from the root, the latter 

 cannot vegetate, while the growth of the crown itself is 

 not thereby prevented. 



As regards internal structure, the root closely resem- 

 bles the stem, and what is stated of the latter, on subse- 

 quent pages, applies in all essential points to the former. 



§•2. 



THE STEM. 



Shortly after the protrusion of the rootlet from a ger- 

 minating seed, the Stem makes its appearance. It has, 

 in generalj an upward direction, which in many plants 

 is permanent, while in others it shortly falls to tlie 

 ground and grows thereafter horizontally. 



All plants of the higher orders have stems, though in 

 many instances they do not appear above ground, but 

 extend beneath the surface of the soil, and are usually 

 considered to be roots. 



While the root, save in exceptional cases, does not 

 develop other organs, it is the special function of the 

 stem to bear the leaves, flowers, and seed of the plant. 



