IXTERDEPEXDEXCE OF ORGANISMS 



37 



and are readily distinguishable from animal galls which 

 contain distinct cavities for the occupancy of the gall 

 makers.* 



FIG. 28. A fungus gall ot the "witches broom" type on the 

 smooth sumac (Rhus glabra ) 



*While we commonly speak of the gall insect or fungus as a "gall 

 maker," we are not unmindful that it merely furnishes the stimulus 

 to overgrowth on the part of the plant itself. 



