CHAPTER IV. 

 GROWTH OF ROOT AND STEM. 



38. Direction of growth. In studying the germination of 

 seeds one fact becomes very evident which, perhaps was familiar 

 before, that the root grows downward and the stem upward. This 

 is very important for the plant in order 



that its parts may establish a congenial 

 relation to their surroundings, and be 

 in a position to perform their work, the 

 root in the ground and the foliage shoot 

 in the air and light. When seeds are 

 scattered by natural means or are 

 sown by the farmer or gardner they 

 fall in various positions. The seed 

 may lie so that the embryo is upright 

 and the root already pointing in a 

 downward direction, or it may be hori- 

 zontal or inverted. Nevertheless, the 

 root when it emerges from the seed 

 turns downward to enter the soil, and 

 the stem turns upward. Some seeds 

 which are carried by the wind are so 

 balanced that the root end of the em- 

 bryo hangs downward (many compo- 

 sites, the clematis, etc., see chapter on 

 seed distribution). 



39. Region of elongation in roots. 

 The region where elongation takes 

 place in roots is determined by a care- 

 ful plotting of the root into a number of small sections, and by 

 keeping the seedling in an upright position in moist air. Sub- 

 sequent observations and a careful plotting of the root from 



25 



Fig. 30. 



Pumpkin seedlings, the root 

 marked in left. Right one show- 

 ing where growth took place in 

 twenty-four hours. 



