DISEASES N^OT DUE TO PARASITES OR OF UNKNOWN ORIGIN II95 



largely to the spread and extension of the disease, as is evident from the 

 experiments carried out with Aphis gossypii Glover (" melon aphid "). 



927 - Mosaic Disease in Cucumbers grown under Glass. — j agger j . c, in Phyt,, pathology. 



Vol. 6, No. 2, pp. 148-151. Baltimore, ]M(i., 1916. 



The sjanptoms of the mosaic disease in plants grown under glass are 

 identical with those found in plants growing in the field. With regard to 

 the effects, on the other hand, they are much worse, which fact is no doubt 

 explained by the lower degree of resistance of plants which have develop- 

 ed in an artificial and enclosed environment. A few days after the appear- 

 ance of the first symptoms the branches wither and die, and sometimes 

 the whole plant dries up. Tests of artificial infection have been made by 

 inoculating varying quantities of sap taken from infected plants into the 

 stalk of healthy cucumbers with a hypodermic syringe. The result was 

 invariably positive. Aphis gossypii Glover contributes largely to the spread 

 of the disease, as was shown b}^ numerous experiments carried out by the 

 writer in the vicinity of Rochester, New York. The infected sap of dis- 

 eased cucumbers inoculated into plants of Cucurhita brought about the onset 

 of the disease. Furthermore the plants thus contaminated, in their turn 

 furnished material which produced the same disease in other healthy cu- 

 cumber plants. 



i^.s - Sour Scab of Citrus Plants in Florida. — 0R03.sE.sri'.ACHEKj- ('..,in Phytopathology, 



\'ol. 6, No. 2, pp. 127-142. Fig. 4. Baltimore, Md., 1916. 



The name of " sour scab " is applied to a disease of the leaves, branches 

 and fruits of certain varieties of Citrus ha\'ing a strongly acid sap in their 

 actively growing portions. 



Citnts Atirantiumvar. amara (sour orange) , C. medicavsLT. Lemon (lemon) 

 and C. medica var. genuina (citron) are very susceptible to the disease, and 

 the same applies to almost all the commercial varieties of C. deciimana var. 

 Pomelo (grapefruit), except perhaps " Triumph " which appears to be a 

 resistant variety. 



The most evident pathological symptoms are the distorted appearance 

 of the leaves and the warty, misshapen fruits. Both on the leaves and on 

 badly diseased fruits, conical elevations with greyish brown tips are found. 

 Some parts of the leaf seem to grow faster than others, which causes the char- 

 acteristic distortion. As the season advances, the warty protuberances 

 flatten out slightly and become scabby. Vinally, if the weather keeps suf- 

 ficiently hot and moist, Cladosporinm Citri develops at the infected spots 

 and produces an enormous quantity of brownish-black spores. 



The severity of the attack varies greatly from year to year and often 

 from tree to tree. Generally this disease is more frequent in the hot and 

 moist seaboard region than in the pine region, which is more inland and at a 

 greater altitude, where plant growth is .slower. 



On the other hand, when the weather is cold and wet at the beginning 

 of spring this disease appears even in groves in high-pine land, especially 

 if there has been an excessive use of nitrogenous manure. 



Good results mav be obtained, however bv in(li\'idnal selection of verv 



