A TRIBE OF WEED WAIilUORS 217 



are gone, strawberries are ripe, and there is plenty of 

 food and shelter for birds here. Bnt if we were to travel 

 northward, beyond the United States and up through 

 Canada, we should find that the trees were different ; 

 that there were more pines and spruces. Then if we 

 went still further north, even these would begin to 

 grow more scanty and stunted, until the low pines 

 in which the Grosbeak nests would be the only trees 

 seen. Then beyond this parallel of latitude comes the 

 ' tree limit ' — " 



" Oh, I know what a ' parallel of latitude ' is, because 

 I learned it in my geography," said Dodo, who had 

 been pouting since Nat teased her about the cracked 

 ice ; " it's a make-believe line that runs all round the 

 world like the equator. But what is a ' tree limit ' ? " 



" Don't you remember, little girl," answered the Doc- 

 tor, " what I told you about the timber-line on a moun- 

 tain — the height beyond which no trees grow, because 

 it gets too cold for them up there ? It is just the same 

 if you go northward on flat ground like Orchard Farm ; 

 for when you have gone far enough there are no more 

 trees to be seen. In that northern country the winter 

 is so long and cold, and summer is so short, that only 

 scrubby bushes can grow there. Next beyond these 

 we should find merely the rough, curling grass of the 

 Barren Grounds, which would tell us we were approach- 

 ing the arctic circle, and already near the place where 

 wise men think it is best to turn homeward ; for it is 

 close to the Land of the Polar Bear and the Northern 

 Lights — the region of perpetual snow. But dreary as 

 this would seem to us, nest building is going on there 

 this June day, as well as here. 



