86 



Journal of Agricultural Research 



Vol. VI, No. 3 



hyalin, and 9 to 1 2 by 3 to 4)U. They germinate within 24 hours in water 

 or in a variety of culture media. A white mycelial growth is produced 

 on bean agar. Pycnidia are readily formed on agar (PI. XI, fig. 3) 

 modified by the addition of a water extract from corn meal, rice, cowpeas, 

 orange stems, etc. (fig. 8). 



The fungus, furthermore, was very probably introduced into the 

 United States similtaneously with Pseudomonas citri. It is impossible to 

 determine the position of this organism among previously described 

 species, since it has been found to be morphologically not unlike several 

 of them. Its relation to the production of Citrus canker is definitely 

 established as a result of this study. Then, too, no particular difficulty 

 would be experienced by other investigators in identifying it because of 



its association with 

 Citrus canker. In 

 view of these facts it 

 seems well to de- 

 scribe it as a new 

 species with the fol- 

 lowing brief technical 

 diagnosis : ^ 



Phoma socia, n. sp. 



Pycnidia irregularly 

 distributed, globose, 

 wholly or partially em- 

 bedded, 100 to 150M in 

 diameter; walls thin, 

 corky brown in color, 

 thickened only around theostiolum, which opens centrally; conidia continuous, ellip- 

 tical or oblong, hyalin, 9 to 12 by 3 to 4ju. 



Occm-s in the cankers produced by Pseudomonas citri on living leaves and branches 

 of Citrus trifoliata, C. nohilis, and Fortunella sp. and on living leaves, branches, 

 and fruits of C. decumana and C. aurantium. 



Fig. 8. — a. Cross section of a pycnidium of Phoma socia from a grape- 

 fruit leaf. This material was fixed in chromo-acetic acid, embedded 

 in parafiin, sectioned, and stained in saffranin and gentian violet. 

 Drawing outlined with the aid of a camera lucida. 6, Germination 

 of conidia of Phoma socia after 24 hours in water, c. Mycelium of this 

 fungus in old cultures. 



ACIDITY AND RESISTANCE TO CANKER 



It is generally conceded by both nurserymen and growers and has been 

 substantiated by the field observations of the writer that Satsuma oranges 

 are not as susceptible to Citrus canker as grapefruit. This difference 

 may be noted when both species are grown in locations where they are 

 equally exposed to infection. The tolerance of bacteria to acidity has 

 been found to be relatively low. Resistance to certain fungus diseases, 

 as, for example, the resistance of hard wheat to rust, has been found (3) 



1 Phoma socia, sp. nov. 



Pcrithedis irregulariter distributis, globosisplus minusve immersis, loo to i^oMdiam.; contextu mem- 

 branaceo.corticale-brunneo.cumcellulis circa ostiolum pseudoparenchymatids, centro perf oralis ; sporulis 

 continuis, elUptids v. oblongis, hyaUnis 9-12 X 3-4M. Hab. in foliis ramisque, vivis Citri irifoliatae, 

 C. nobilis et Fortunellae sp. et quoque in foliis, ramis fructibusque C. decumanae et C. aurantii. Socia 

 adest Pseudomonas citri Hasse. 



