320 Journal of Agricultural Research vol. xx.no. 



cultivation in February were observed to have less of the disease than 

 neighboring fields which had not been so treated. There was ample 

 evidence that the disease had been severe in these fields in the previous 

 season. However, in the following spring the difference between culti- 

 vated and uncultivated fields had disappeared. 



There is a limited amount of field evidence that the amount of dis- 

 ease is increased when alfalfa is planted directly after alfalfa. Fortu- 

 nately, such succession is rarely practiced. Thus, on the whole, it can 

 be said that when conditions are made most favorable for the develop- 

 ment of the alfalfa plant the disease is diminished, perhaps not so much 

 because the plant is better able to withstand its attacks as because 

 abundant infection is dependent upon conditions which are not of them- 

 selves most favorable for plant development. 



Search has been made in vain for any evidence of conspicuous cases 

 of apparent resistance to the disease. In one instance in 191 9 a plot 

 of alfalfa was found conspicuously freer from the disease than the adjoin- 

 ing plots which appeared to be under exactly the same conditions. It 

 was found that the seed used in this plot was from a different source 

 than that used in the other plots, and in fact the type of plant was 

 different. An effort to obtain seed from this field for experimental 

 work was frustrated by the ravages of grasshoppers. During the fol- 

 lowing year observation failed to discover any material difference in 

 the amount of disease in this field as compared with its neighbors, and 

 therefore efforts to obtain seed from it were abandoned. 



It hardly need be said that until it is known for a certainty whether 

 the disease can be troublesome in the eastern alfalfa-growing regions, 

 care should be taken to prevent its introduction. At least living plants 

 from fields where the disease is known to occur should not be trans- 

 ported to other localities. 



SUMMARY 



The disease of alfalfa caused by the fungus Urophlyctis alfalfae, com- 

 monly known as crownwart, has been found to have its origin in the 

 infection of very young buds, the foliar elements of which develop into 

 abnormalities not involving the mature structures of root or stem. 



Infection appears to take place only early in the spring, becoming 

 easily discoverable in the latter part of March or in early April in 

 northern California. 



In irrigated regions, or in regions where there is abundant moisture 

 during the entire season, most of the galls reach full development early 

 in the summer and thereafter decay rapidly, only a few surviving until 

 the next spring. 



The thallus of the fungus consists of two types of structures, turbinate 

 cells and resting spores. In the first turbinate cell that is the imme- 

 diate development of the infecting fungus are inserted a number of septa 



