PLANTS THAT TELL TIME 109 
“and, departing, leaves behind it” a record for the 
instruction and inspiration of future generations. 
The trunk of an alder is as truly an autobiogra- 
phy as are those written of themselves by the hands 
of men. And to one knowing and understanding 
the meanings of its various recording marks, the 
story is as clear as if recorded on the pages of a 
book. 
For each year of its life the cross-section of a 
tree trunk shows a ring. This is the diary for that 
year. Is there a deep depression in one side of that 
fourth year’s record? Perhaps a fallen log pressed 
against it there, temporarily hindering the tree’s 
growth on that side. Do you notice that one side 
of the trunk is bulkier than the other? That is 
the southern side, where the warm sun by swelling 
the veins has correspondingly increased the thick- 
ness of growth. Look at the opposite side and you 
will see that the bark is thicker than on the south- 
ern side. The tree has clothed itself more warmly 
against the cold north winds than against the warm 
southern sun; and on this side too you will find an 
overcoat of green moss—an additional protection 
against cold. 
How many times have we stood beneath some 
ancient tree and, looking up, cried hopelessly, “Oh, 
if you could only tell us what you have seen in all 
