WHITE-PIXE BLISTER RUST. 35 



fected area. They must have been produced by aeciospores which 

 had been blown at least the above distances. 



In 1919, York caught and germinated eeciospores on the summits 

 of two mountains nearly 4,300 feet above the adjoining lowlands. 

 It is evident that altitudes such as this do not prevent the spread 

 of this fungus. Pennington ^* caught aeciospores up to 1,200 feet 

 distant from pines and found diseased Ribes three-fourths of a mile 

 from any pine tree. 



AGENTS DISSEMINATING THE ^CIOSPORES. 



It has been evident from the beginning that wind is a most efficient 

 and active agent in the distribution of the spores of Cronartium 

 rihicola. While the probability of spore carriage by other agents 

 such as insects and the larger animals was recognized, no time could 

 be spared for work upon it. More recently, Gravatt and Marshall 

 (46) and Gravatt and Posey (46) have made some studies of this 

 sort. 



Gravatt and Marshall worked in the experimental greenhouse 

 where no aecia were present. They found that pycnia and the 

 surrounding bark tissues were eaten by sow bugs. 



Gravatt and Posey (46) made studies in the field in a heavily 

 infected pine area at Kittery Point, Me. Here it was found that 

 gipsy-moth larvae, which were abundant, fed eagerly on the 

 pycnia and secia of the blister rust and also ate the bark tissues 

 immediately adjacent to them. It was found that in some cankers 

 a considerable percentage of the fruiting secia were thus destroyed. 

 But a few: ingested spores remained viable, as tests in hanging drop 

 cells in tap water yielded a few germinations. These larvae also 

 were carriers of abundant aeciospores on their bodies, many being of a 

 decided yeUow color from the spores with which they were dusted. 

 The gipsy-moth larvae are knowTi to have been blowTi 20 miles or 

 more. Within the gipsy-moth infested area these larvae are then 

 dangerous agents in the distant spread of the disease, a fact not 

 previously appreciated. 



Notes made by Gravatt show that a wood mouse caught in the out- 

 break area at Kittery Point, Me., carried a small number of asciospores 

 on its body. While squirrels, other animals, and birds have not been 

 examined, there can be no doubt that they are active carriers of the 

 spores. It is known that the a)ciospores become attached readily 

 to clothing, and there can be no doubt that persons may carry the 

 disease, at least locally, in this manner. 



In a number of outbreak areas where pine infections were just about 

 to produce pycnia for the first time, it was noted by several observers *" 



IS Pennington, L. H. Op. eit. 

 " Rhoads, A. S. Op. cU. 



