284 FIRST YEAR COURSE IN GENERAL SCIENCE 



seeds into the crevices of the rock on which the plant grows. 

 The flower of the peanut plant opens and is pollinated in 

 the light, but after pollination its stalk turns downward and 

 pushes the young seed pod into the ground, where it ripens. 

 Although peanuts are pulled from the ground, they are not 

 roots nor stems, but ripened ovaries and seeds. 



326. The Influence of Gravity. We are not surprised 

 to learn that plants make use of a constant and universal 

 force such as gravity in guiding their 

 organs into suitable positions. The 

 fact that roots grow downward is so 

 familiar that we do not usually think 

 of it as needing explanation. No 

 matter in what position a bean seed 

 is planted, the primary root will grow 

 down and the stem up. We could 

 demonstrate that the direction of 

 growth is determined by gravity if we 

 could study a plant in some region 

 where gravity did not exist. This, of 

 course, cannot be done; but we can 

 These beans were all place several germinated seeds with 

 the root tips pointing in different di- 



FIG. 151. THE INFLU- 

 ENCE OF GRAVITY 



sprouted under the same 

 conditions and were 



placed, when the sprouts rections and watch their growth. 



were very short, between -p, -, . r ,1 i ,, 



moist blotting paper and Be a P iece ot wet blotting paper 



glass, i. Describe the to fit the inside of a tumbler like a 



change of direction in r , 



some of the sprouts. 2. in hning. Place several germinated 

 which cases has there been beans or peas between the paper and 



no change of direction? ,v i ,-, .-, . .. 



3. What conclusion in re- tne S lass > One Wlth the root Pointing 



gard to the influence of up, one to the right, one to the left, 



gravity could be drawn -, -, i -i T 



from these two answers? one downward, and others in different 

 directions. After a few days every 



tip will point downward, some roots having made a short 

 turn, and some having wound around the seed before it 

 was possible to turn downward. 



