No. 2, June, 1921] PATHOLOGY 195 



THE PATHOGENE (BIOLOGY; INFECTION PHENOMENA; DISPERSAL) 



1353. Fawcett, H. S. Pythiacystis and Phytophthora (on Citrus). Phytopath. 10: 397- 

 399. 1920. — Cultures obtained from fruit and diseased bark of one type of gummosis of citrus 

 in California were mostly Pythiacystis citrophthora Sm. and Sm.; cultures made from dis- 

 eased bark of "footrot" from various sources all gave Phytophthora terrestria Sherbakoff. 

 Pythiacystis-like forms were obtained from other hosts in California. — R. B. Streets. 



1354. Hedgcock, George G., and N. Rex Hunt. Notes on Peridermium harknessii. 

 Phytopath. 10: 395-397. 1920.— Field observations of the spread of the aecial stage of Peri- 

 dermium harknessii, apparently without the aid of the telial host, are confirmed by experi- 

 ments with several species of pine in which a true aecial stage follows inoculation with aecio- 

 spores. — G. Wineland. 



1355. Jagger, Ivan C. Sclerotinia minor, n. sp., the cause of a decay of lettuce, celery, 

 and other crops. Jour. Agric. Res. 20: 331-333. PL 59, 1 fig. 1920 [1921].— A technical de- 

 scription of *S. minor with illustrations of apothecia, ascospores, and microconidia. Apothecia 

 and sclerotia of S. libertiana are much larger. The fungus causes a decay of lettuce and 

 other plants similar to that produced by S. libertiana. It is known to occur in Massachusetts, 

 New York, Pennsylvania, and Florida. — D. Reddick. 



1356. Matz, J. Infection and nature of the yellow stripe disease of cane (mosaic, mott- 

 ling,etc.). Jour. Dept. Agric. Porto Rico 3^: 65-82. 1919 [1920].— Cuttings from cane showing 

 mosaic were used for propagating purposes. New shoots from such pieces invariably showed 

 symptoms of the disease. The canker stage of mosaic has been secured in as short a time as 

 3" months.— Transmission experiments by contact failed. Hypodermic injections of juice 

 from diseased plants gave infection in 4 cases of over 200 trials.— Histological studies of dis- 

 eased and healthy plants were made. "It seems that a foreign plasmodium-like substance 

 is apparently present in the cells of the yellow-striped cane leaf and the stem tissue. "This 

 plasmic substance is more constantly present and in a more defined form in cankered cane 

 stalks. It is associated with reddish streaks that may be seen on the interior of severely 

 affected cane. The plasma mass becomes granular in cut pieces and "after eight days motility 

 was observed in the plasma mass." The substance resembles a plasmodium.— D. Reddick. 



1357. Peltier, George L. The influence of temperature and humidity on the growth of 

 Pseudomonas citri, and of its host plants, and on infection and development of the disease. 

 Jour. Agric. Res. 20:29.5-323. PI. 47-56. 1920 [1921].— The temperature relations of P. 

 citri, in culture, are similar to other pathogenes of the Pseudomonas group. The factor of 

 time should receive more consideration. When it is considered, the critical temperature in 

 degrees Centigrade are as follows: Minimum, 5; optimum, between 20 and 30; maximum, about 

 35; thermal death point, between 49 and 52.— Humidity has little or no influence on the via- 

 bility of the organisms at low temperatures but at high temperatures it is the limiting factor. 

 With medium humidities "at all temperatures, the organism is viable for the period of the 

 experiment." "Some factor or factors, other than the rapidity of drying, are responsible for 

 these results."— Citrus plants under controlled conditions vary markedly in their reaction to 

 temperature and humidity, especially at low and at high temperatures. The optimum tem- 

 perature for the plants used lies between 20 and 30°C. This condition, with slight varia- 

 tions, also prevails in the field.— Infection depends on 3 conditions: Free moisture on the 

 host, suitable temperature, host in actively growing condition. The organism is active m 

 the tissue so long as the host cells are active. When the host is forced into dormancy the 

 organism becomes inactive. The "period of initial infection" is defined as the time required 

 by the pathogene after it reaches the host to enter the stomates or tissues about a wound. 

 This may occur on plants which are not growing actively. The ''period of incubation" extends 

 from the time of initial infection until there is visible evidence of disease. This period there- 

 fore depends on the conditions of the host at the time of, and immediately following, initial 

 infection. Frequency of rainfall and the temperature each in a dual relation determine 



