Began growing 

 550 A. D. 



~ Goths expelled from Italy 



60(321 Pope Gregory 



800— 



Time of Mohammed 



900 Norsemen to England 



William tke Conqueror (1066) 



HOQ-— 



5 Rrst Crusade 



1200— Magna Carta (1215) 



1300— 



1400— 



1500 — 

 1600— 



Mariner's compass 



Columbus discovers America 



Lanang^rf Mayflower (1620) 



-^^13feClarauOT"Ci inue|Mil'iuence 



Pagteur 



• Cut in 1891 



This giant tree was 1341 years 

 of age at date of cutting 



Diameter 16^2 ft (inside bark) 



Circumference — 52 ft (approx.) 

 Height 250 ft (approx.) 



American Museum of Natural History 



LIGHT AND LIFE 



Variations in the rings of a tree's wood evidently correspond to yearly variations in 

 conditions favorable to growth. But these variations appear to be periodic; and the 

 rhythm corresponds in a remarkable degree to the rhythm of sunshine intensity, 

 which in turn is related to the sunspot cycle of about eleven years 



we are so much better prepared to deal with them. If the scale-lice, for exam- 

 ple, cover the twigs of a tree in a thick layer, the ladybird beetles will de\our 

 them voraciously, and then multiply very rapidly. The happy and prosperous 

 plant lice are all but wiped out. Their very prosperity has invited an epidemic 

 of their enemies. An epidemic may in fact be considered as a very prosperous 

 opportunity for some plant or animal that unexpectedly gets into a crowd of 

 its potential hosts or victims. 



581 



