254 PATHOLOGY [BoT. Absts., Vol. IX, 



on the proper pabulum, (4) their gieat abundance, and (5) the provisions for their wide dis- 

 semination," the ascospores are the main source of infection. The conidia are produced in 

 enormous numbers and may appear the first or any subsequent season. They are quickly 

 killed by drying and probably cause but little infection, for repeated failures have resulted 

 from attempts to cause infection under natural conditions. The mycelium is capable of caus- 

 ing infection but it is probable that such infections are rare. The manner of infection is 

 influenced by disseminating agents such as water, wind, insects, pruning tools, etc.; by 

 the opportunity for infection such as is occasioned by the presence of large wounds on older 

 wood; and by the physical conditions such as age and vigor of tree and weather conditions, the 

 canker being more prevalent on older trees and during dry seasons. The mycelium grows 

 rapidly in the dry wood and may extend several feet from the apparent canker. — In Illinois 

 the chief varieties injured are Ben Davis, Gano, Chenango, and Willow Twig. The author 

 thinks that with the elimination of Ben Davis there would be but little trouble from the 

 disease. Wild hosts, especially the mountain ash, should also be destroyed. — The author gives 

 a plan for the practical control of blister canker which includes avoiding susceptible varieties, 

 removing diseased young trees, and disinfecting and carefully pruning all diseased trees in 

 order to destroy all ascospores. — H. W .' Richey. 



1551. Chemix, E. Action d'un champignon parasite sur DilseaedulisStackhouse. [Effect 

 of a fungus parasitic on Dilsea edulis.] Compt. Rend. Acad. Sci. Paris 172: 614-617. 1921. — 

 A description is given of the effect of parasitic fungi upon the plants of this red alga. The 

 author discusses the parasitism and symbiosis of fungi living in association with algae. — 

 C. H. Farr. 



1552. McLean, Forman T. A study of the structure of the stomata of two species of Citrus 

 in relation to citrus canker. Bull. Torrey Bot. Club 48: 101-lOG. 1 fig. 1921. — Stomata 

 of Szinkum mandarin, which is resistant to Citrus canker {Pseudomonas citri), and of Florida 

 seedling grapefruit, which is susceptible, are compared and those of the resistant form are 

 found to have a broad ridge of entrance overarching the outer chamber. Such an arrangement 

 practically excludes water from the stomata of the mandarin and accounts for resistance to 

 canker bacteria. — P. A. Munz. 



1553. McLean, Forman T., and H. Atherton Lee. The resistance to citrus canker 

 of Citrus nobilis and a suggestion as to the production of resistant varieties in other citrus 

 species. Phytopathology 11: 109-114a. Fig. 1. 1921. — The horticultural varieties of the 

 Mandarin orange {Citrus nobilis var. deliciosa) have been mentioned by various writers as 

 truly resistant to canker (Pseudomonas citri). The fact that a few scattered cankers fre- 

 quently occur on trees of these varieties led to an investigation of the resistance of the latter. 

 Inoculation with pure cultures of Pseudomonas citri were made upon wounded and unwounded 

 leaves of three varieties of this group. The inoculation of wounded leaves gave a percentage 

 of infection fully as high as with the more susceptible species of Citrus; while with the un- 

 wounded leaves only a few cankers developed, evidently at insect or other punctures. The 

 results indicate that the resistance is due to the nature of the epidermis (see preceding entry). 

 The utilization of graft hybrids, to transfer the Mandarin epidermis and resistance to other 

 more susceptible varieties without changing the quality of the fruit, is suggested. — B. B. 

 Higgins. 



DESCRIPTIVE PLANT PATHOLOGY 



1554. BiJL, Paul A. van der. On a fungus, Ovulariopsis Papayae n. sp., which causes 

 powdery mildew on the leaves of the pawpaw plant (Carica Papaya L.). Trans. Roy. Soc. South 

 Africa 9: 187-189. PI. 10, 1 fig. 1921. — A description is given of the fungus which is thought 

 to be the conidial stage of a Phyllactinia. — E. M. Doidge. 



1555. Carpenter, C. W. Report of the Division of Plant Pathology. Hawaii Agric. 

 Exp. Sta. Rept. 1919: 49-54. PL 7-S. 1920.— Discussion of taro rot (probably Pythium 

 deBaryanum), taro stem rot {Sclerotium rolfsii), and of the control of banana freckle disease 



