REPORT OF THE SOCIETY 51 



slightly affected that it is difficult to tell with certainty whether mosaic is 

 really present. Some of our highest yielding fields have had considerable 

 mosaic. The problem of handling this disease is a very real one in New 

 York where we are endeavouring to certify high-grade healthy seed and yet 

 not exclude high-yielding stock. 



Streak is another disease that produces a condition somewhat similar 

 to those already mentioned in that the plant becomes much dwarfed and 

 weakened. The writer's first experience with this disease, as he diagnosed 

 it, was with tubers sent us fro'm Idaho by Dr. H. A. Edson of the United 

 States Department of Agriculture. These tubers came from plants having 

 leaf roll and were sent that we might observe leaf-roll characters. About 

 a month after the plants had appeared, one plant at the end of the row 

 which had been much dwarfed from the time it appeared showed a spotting 

 of the foliage similar to early blight. This was first thought to be the 

 trouble, but a closer examination showed dark streaks in the petioles and 

 the stalks. The petioles were so brittle that they broke in two readily 

 when the leaves were touched and the stalks were easily broken also. Later 

 the leaves died, beginning with the lower ones, so that after a time there were 

 but a few small green leaves at the apex. The entire plant died much 

 earlier than normal ones and the few tubers produced were the size of 

 marbles. 



Not long after the discovery of the first a second and then a third plant 

 from the Idaho seed were found affected in this same manner. For a time 

 this was thought to be a character peculiar to leaf roll but this opinion 

 changed when the spotting of the leaves was found on vigorous Evergreen 

 potato plants growing in a row adjoining those mentioned. These Ever- 

 green potatoes had been grown in the diseased garden for the two preceding 

 years in order to test their reputed resistance to late blight, but the spotting 

 described had never been observed on them. It seemed evident then that 

 the disease is infectious. This surmise was strengthened by the spread of 

 the disease to several other Evergreen potato plants. However, an attempt 

 to obtain an artificial infection by the inoculation of healthy plants with 

 bacteria obtained from a culture made from an affected stem was without 

 success. 



The Evergreen plants affected, while they showed the same leaf spots 

 as the Idaho plants and showed a similar streaking of petioles and stems 

 followed by early death of affected parts, did not have the dwarfed appear- 

 ance as the vines were large before the infection showed. Some were 

 affected at first on but a single stalk but the other stalks became affected 

 later, and in all cases the decline of the vine after infection was rather rapid. 



