20 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



Fig. 23. — Crown gall, caused by bacteria, occurs usually at the base of 

 an aflfected stem or on the large roots. The gall shown here is on a root. 



Fig. 24 (left). — This elm is affected with dieback, as shown by the many 

 branches with dead tips. 



Fig. 25 (right). — Witches'-broom of hackberry is most conspicuous when 

 the trees are without leaves. 



