142 Our Field and Forest Trees 



work underground also at this season, making 

 large vessels and tubes just below the surfaces of 

 the big, woody roots. 



Later in the year, when life is not quite so 

 vigorous in the forest, smaller vessels and tubes 

 are formed. So the difference between " spring 

 wood " and " summer wood " is easily seen, often 

 with unaided eye, and always with a pocket lens. 

 We may notice this difference on the top of any 

 stump. Spring wood often 

 looks as if it were full of 

 pin-pricks, because we see 

 in it so many round holes, 

 which are the ends of 

 large vessels and tubes — 

 now all empty. The sum- 

 mer wood is much closer 

 and more compact, and 

 Fig. 34. Top of a stump show- often it is darker in color. 



mg the growth rings. 



So rings run around the 

 top of the stump, and by counting these we can get 

 an idea of the age of the tree, but cannot tell it 

 exactly (Fig. 34). For it is quite possible, if the 

 summer is rainy and the autumn warm, that more 

 than one ring will be formed in one year. Some- 

 times, too, summer growth is checked by drought 

 or by unseasonable cold, and begins again when 

 heavy rains fall, or when warm weather returns. 

 In such fitful summers, some enterprising young 

 trees may make half a dozen fresh starts. 



