ECOLOGY or FUNGI 73 



than those on normal twigs. Witches' brooms are found on such conif- 

 erous trees as the white cedar in New Jersey and are due to Gymno- 



FiG. 22. — Black knot of plum, Plowrighlia morbosa, on beach plum, Priinus marilima 

 Nantucket, August 17, 1915. 



Sporangium Ellisii, a rust fungus. These malformations occur on the 

 hackberry, but on this tree they are due to the attack of a mite Phy- 

 toptus followed by a fungus. Plum pockets are a form of gall in which 



