Nov. i 5 , 1920 Crownwart of Alfalfa Caused by Urophlyctis alfalfae 317 



like stem bundles in giving rise to secondary thickening, producing ir- 

 regular masses of leaf elements. Thus, the normal limitation in the 

 direction of cell division and growth which produces thin, laminated 

 structures is removed, and thick, fleshy amorphous masses of tissue 

 inclosing ramifying cavities filled with the fungus in all stages of de- 

 velopment are produced. On irrigated land these structures are not 

 usually well protected by epidermis or cortex and readily dry out or decay, 

 but in dry regions many become covered with a corky layer that pro- 

 tects them from destruction. 



In partial contrast to the galls upon alfalfa is the gall upon Sanicula 

 menziesii (PI. 53) caused by Urophlyctis pluriannulatus previously men- 

 tioned, a contrast indicated by Magnus (79) in his classification of Uro- 

 phlyctis galls into two types, those upon underground parts of plants 

 and those upon aerial parts. Although the earliest stages in the forma- 

 tion of these galls have not been traced, evidence from more mature 

 stages indicates that the general development is similar to that of galls 

 formed on alfalfa and in fact is exactly like that of the blister-like galls 

 sometimes found on alfalfa leaves. In the attack of the fungus on Sani- 

 cula, infection of the leaf, petiole, and stem structures takes place at a 

 later stage of host development than is common on alfalfa, and the re- 

 sponse of the host tissue to the stimulus of the fungus is not nearly so 

 great, extending only to a distance of a few cells. Apparently a small 

 number of cells are rapidly invaded soon after the fungus enters the host. 

 Thickening of the host cell walls around the cavity formed, especially its 

 basal portion, soon occurs ; and thereafter it appears that a part at least 

 of the enlargement of the fungus cavity is accomplished by the pressure 

 of the growing fungus mass against the surrounding cells, which become 

 flattened and distorted. Thus, each infection produces one partly cham- 

 bered cavity in the parenchymatous tissue which has become hypertro- 

 phied to form a small blister-like gall. 



INOCULATION EXPERIMENTS 



In order to avert any possible danger of spread of the disease from 

 experimental plots, inoculation experiments were limited to a few potted 

 plants in a greenhouse at Washington and to plants in the greenhouse 

 and on the trial grounds of the United States Plant Introduction Garden 

 at Chico, Calif. At the latter place, perhaps because of the limited time 

 during which work was done there, no success was attained in producing 

 infection. Since one of these failures may be significant, it will be men- 

 tioned. On April 15, 191 8, nine days after wart was first found devel- 

 oping on plants in the field, an inoculum was prepared by shaking soil 

 and the fragments of decomposed warts from the crowns of a large num- 

 ber of plants which had been badly diseased the previous year and adding 

 a small amount of crushed warts which had been found not yet decayed. 



