256 



Journal of Agricultural Research 



Vol. Xin, No. 4 



the sense in which this term is applied by animal pathologists in that 

 they are not multinucleate, but remain uninucleate. The yellowish or 

 whitish appearance of the protrusion is accounted for by the fact that 

 the intercellular spaces are filled with air. 



Fig. I.— Outline drawing, made with the aid of a camera lucida, of a vertical section of an intumes- 

 cence on cabbage. 



Since neither fungi nor bacteria were associated with these intumes- 

 cences, it was conceived that they must have resulted from injuries 

 inflicted by wind-blown sand. This deduction was subsequently con- 

 firmed both under field and greenhouse conditions by violently projecting 

 sand against normal cabbage plants. Intumescences of the type shown 

 in figure B of Plate 18 developed within four to six days following the 

 wounding. The intumescences thus artificially produced were identical 

 in appearance and structure with those first found. They could not be 

 made to appear upon mature parts, but only upon actively growing 

 tissues. They occurred both on the lamina of the leaf and upon the 

 veins. In the latter case the xylem elements were not modified, the 

 only modification occurring in the parenchymatous cells surrounding the 

 vascular bundles. Sections through intumescences upon small veins 

 showed that the normal vascular elements may be entirely surrounded 

 by hypertrophied cells. 



Humidity was observ^ed to operate in conjunction with the age of the 

 tissues in the development of intumescences. When a plant injured by 

 sand cast upon it was covered with a bell jar in order to maintain a high 

 relative humidity, the edematous cells continued to enlarge until the 



