THE MOSAIC DISEASE OF TOBACCO. 17 



of inoculation and the appearance of the first mosaic symptoms. 

 Mayer 2 produced the disease in 10 to 12 days. In the writer's experi- 

 ments the shortest period elapsing between inoculation and the 

 expression of the first visible symptoms was six to seven days. In ex- 

 periments during the years 1912 and 1913 many hundreds of tobacco 

 plants were inoculated with the mosaic virus at all stages of growth, 

 from the appearance of the cotyledons to complete maturity. The 

 results of some of these inoculations are as follows: 



Ten good-sized plants of several American varieties of tobacco inoculated on 

 November 18, 1912. First symptoms noted in 16 to 17 days. 



Five plants of Nicotiana tabacum 9 X N. glauca $ inoculated on December 

 8, 1912. First symptoms noted in 14 to 15 days. 



One hundred good-sized plants of N. tabacum 9 X N. silvestris $ inoculated 

 on December 8, 1912. First symptoms appeared in 10 to 11 days. 



Four young plants of N. tabacum $ X N. glauca $ inoculated on December 

 12, 1912. First symptoms noted in 12 days. 



Six ratber large plants inoculated on December 16, 1912. First symptoms 

 appeared in 20 days. 



Twelve plants of N. tabacum 2 X N. silvestris $ inoculated on December 16, 

 1912. First symptoms noted in 20 days. 



Nine Broadleaf plants inoculated on December 21, 1912. First symptoms 

 appeared in about 15 days. 



Nine young plants of Connecticut Broadleaf inoculated on December 26, 1912. 

 First symptoms appeared in 11 days. 



Twelve full-sized, nearly mature tobacco plants inoculated on February 8, 

 1912. First symptoms noted in 12 to 15 days. 



Sixty-six small tobacco plants inoculated on May 8, 1912. First symptoms 

 were showing in nearly every plant on May 14 to 15, i. e., 6 to 7 days following 

 inoculation. 



Eight plants of Nicotiana paniculata inoculated May 10, 1912, showed first 

 observable symptoms 20 days later. 



Twenty-nine young tobacco plants inoculated on June 14, 1912, showed first 

 observable symptoms in practically all within 9 to 10 days. 



Seventy young, vigorous tobacco plants inoculated on March 28, 1912, showed 

 first observable symptoms in 6 to 7 days. 



Thirty young plants inoculated on December 9, 1912, showed practically every 

 plant diseased January 10 to 11, about 30 days later. These plants were grown 

 in a very cool greenhouse, so that the rate of growth of the plants was very slow. 



Thirty young. plants inoculated on January 4, 1913, showed first symptoms 

 18 to 20 days later. 



Six or seven days probably is about the minimum period required 

 to show the first visible mosaic symptoms in tobacco at whatever 

 stage of growth the plants are inoculated. The disease manifests 

 visible symptoms usually after 12 to 15 days. Low temperature con- 

 ditions that generally retard growth appear indirectly to retard the 

 visible expression of symptoms, which are usually associated with 

 actively growing cells and tissues. 



1 Mayer, Adolf. Op. cit. 

 13128°— Bull. 40—14 3 



