102 
WORLD OF INVISIBLE LIFE 
What are the 
rings in wood? 
We also notice that there are rings of rather 
large cells with thin walls and then rings of 
smaller cells with thicker walls which alternate 
from the center to the edge of the trunk. They 
make the wood look light and then dark col¬ 
ored. These are the annual rings by which 
we can tell the age of the tree. The wood 
formed in the spring has larger cells with thin¬ 
ner walls, while that formed in the fall has thick 
walled smaller cells. Each ring of thick walled 
cells represents a year in the tree’s life. By count¬ 
ing them we can tell the age of the tree. 
The cells are a little different in the woods of 
different trees. “Hard” woods like maple and 
oak have thicker walled cells, which contain 
more woody substance, while “soft” woods like 
pine and spruce have thin walls and much less 
woody fiber. 
Botanists have found that there are several 
different kinds of roots. Some plants have roots 
which merely hold the plant down to the 
ground and absorb the water it needs. Other 
plants have roots from which the new plant 
