INTUMESCENCES, WITH A NOTE ON MECHANICAL IN- 

 JURY AS A CAUSE OF THEIR DEVELOPMENT ' 



By Frederick A. Wolf 

 Plant Pathologist, North Carolina Agricultural Experiment Station 



INTRODUCTION 



Little attention has been given by plant pathologists to the pustule - 

 like outgrowths of tissue to which the appellation "intumescences" 

 may be appropriately applied. The accounts of them deal mainly with 

 descriptions of their occurrence upon the leaves, flowers, fruits, and 

 twigs of various species of plants and with suggestions regarding the 

 cause, in most cases not supported by experiments. Since no great 

 imaginative power is required to see that the problem of intumescences 

 is merely a part of the greater problem of all excrescences or over- 

 growths in plant and animal tissues, such as galls, tumors, knots, 

 cankers, edemata, crowngalls, etc., intumescences then become of imme- 

 diate interest to both plant and animal pathologists. While the remote 

 or ultimate causes of these overgrowths may be entirely different, inves- 

 tigators of these phenomena do not appear to realize that they are 

 probably dealing with the same proximate cause. This fact is illustrated 

 by studies on insect galls, concerning which an enormous volume of litera- 

 ture has accunmlated; on crowngalls, our knowledge of which is due 

 largely to the illuminating researches of Smith (9, 10, 11)' and his asso- 

 ciates; and on edemata, the cause of which is so clearly demonstrated 

 in the brilliant experimentation of Fischer (5). It is the present pur- 

 pose, therefore, to review briefly the more important contributions 

 dealing with the cause of intumescences, to describe intumescences 

 arising from mechanical injury, and to suggest that their proximate 

 cause is the same as of edema in animals, the explanation of which 

 appears to have been generally overlooked by plant pathologists or has 

 not been regarded by them as applicable to overgrowths in plants. 



HISTORICAL REVIEW 



The designation "intumescentia" appears to have been first applied 

 by Sorauer {12, p. 222), to pustular processes, generally yellow in color, 

 formed upon the surface of leaves. The cells which make up these 

 processes are always more or less enlarged. In explanation of their 

 occurrence he states that they are brought about by such conditions as 



1 Published with the approval of Director B. W. Kilgore, of the North Carolina Agricultural Experiment 

 Station. 



2 Reference is made by number (italic) to "Literature cited," p. 238-239. 



Journal of Agricultural Research. Vol. XIiI, No. 4 



Washington, D. C. Apr. 22, 1918 



nc (253) ^^y ^°- ^- C-io 



