30 THE GROWTH AND PARTS OF PLANTS 
pull the root down in the same way in which it acts 
on the stone or apple. It only influences or stimulates, 
we say, the root to turn. (If desirable the teacher can 
explain or dem- 
onstrate for the 
pupils, tis 
when the influ- 
ence of gravity 

Fig. 55. Marrow seedling placed horizontally and root tip + . 
cut off to show that without the root tip the root will 1S neutralized, 
seas the root does not 
turn downward but continues to grow in the direction 
in which it was placed. This may be demonstrated by 
the well-known experiment of fastening, in different 
positions, several seedlings on a perpendicular wheel or 

Fic. 56. Bean seedling treated as the marrow seedling in Fig. 55. 
disk which revolves slowly. The position of the root 
with reference to the earth is constantly altered, and 
the influence of gravity is neutralized.) 


