176 MANUAL OF TREE DISEASES 



the diseased condition and may be jointly responsible for the 

 deformation. Two such intimately associated agents, one an 

 insect and the other a fungus, are unusual and deserve more 

 careful study than has been given them. Practically nothing 

 is known concerning the life history of these two parasites and 

 their interrelations, more than has been discussed under symp- 

 toms. Both conidia and perithecia are formed by the mil- 

 dew fungus. The structure, life history and control of the 

 powdery mildew fungi are more fully discussed on page 34. 

 In the case of this disease, control measures seemingly would 

 be confined to cutting out the diseased twigs and brooms. 

 Spraying or dusting could not be expected to yield satisfactory 

 results. 



References 



Kellerman, W. A., and Swingle, W. T. Branch knot of the hackbeiry. 



In Report of the Botanical Department. Kansas Agr. Exp. Sta. 



Ann. Rept. 1 : 302-315, pis. 4r-6. 1889. 

 Halsted, B. D. Notes upon Sphserotheea phytoptophila KeU. and 



Swingle. Jour. Mycology 5:85-86. 1889. 

 Salmon, E. S. Sphssrotheca phytoptophila Kellenn. and Swingle. 



In A monograph of the Erysiphaceae. Mem. Torrey Bot. Club. 



9 : 76-79. 1900. 



