TREES TOLD BY THEIR FORM 



53 



near the surface, upset the sidewalk or prevent the growth 

 of other vegetation on the lawn, while its finer rootlets, 

 in their eager search for moisture, 

 penetrate and clog the joints of 

 neighboring water and sewer pipes. 

 The tree is commonly attacked by 

 the oyster-shell scale, an insect which 

 sucks the sap from its bark and which 

 readily spreads to other more valuable 

 trees like the elm. The female form 

 of this tree is even more objectionable 

 than the male, because in the early 

 spring the former produces an abun- 

 dance of cotton from its seeds which 

 litters the ground and often makes 

 walking dangerous. The only justifi- 

 cation for planting the Carolina 

 poplar is in places where the con- 

 ditions for tree growth are so poor 

 that nothing else will grow, and in 

 those cases the tree should be cut 

 back periodically in order to keep it 

 from becoming too tall and scraggly. 

 It is also desirable for screening in 

 factory districts and similar situa- 

 tions. 



The silver or white poplar (Populus 

 alba) may be told from the other 

 poplars by its characteristic smooth, 

 whitish-green hark, often spotted with 

 dark blotches, Fig. 43. The leaves 

 are silvery-white and downy on the under side. The twigs 

 are dark green in color and densely covered with a white 



Fig. 42.— Bud of the 

 Carolina Poplar. 



