1913.] PUBLIC DOCUMENT — No. 31. 49 



iiig, and as a result the roots arc often lacerated, uneven growth 

 resulting, thus bringing about abmu-nial changes in the proc- 

 esses of plant metabolism. 



It is stated that broad-leaf tobacco is more liable to this dis- 

 ease than Havana, but we have been unable to verify this state- 

 ment locally. 



Shade-grown or tent-groAvn tobacco is said to be less liable to 

 the disease than that grown without shade. This has been our 

 experience and is borne out by the statements of practical 

 growers who have grown both kinds. The conditions governing 

 growth under shade are of course more uniform than in the 

 field, and a more regular and slower development of the plant 

 is brought about. 



Seed. 

 Various investigators have pointed out that the disease is 

 not transmitted through the seed, as it has been shown repeat- 

 edly that seed from mosaic plants will produce healthy plants 

 and vice versa; also that there is no difference in the seed pro- 

 duced by cross pollination as regards susceptibility to the dis- 

 ease, and this has been so repeatedly proved as to need no veri- 

 fication. It is a fact, however, that the heavy seed of tobacco 

 wdll produce larger, better and more uniform plants through 

 careful selection, and as this laboratory has made a specialty 

 of separating the seed for the growers for the last few years, 

 observations on the prevalence of the mosaic were made among 

 the fields each year, and it was found that growers who were 

 having their seed separated each year had less and less trouble 

 with mosaic, due somewhat to the selection of a more vigorous 

 seed. Only the heavy seed was planted, and only the seed of 

 the ])est plants saved; thus a process of seed selection was prac- 

 ticed and naturally an improvement in the quality of the plants 

 was found. The seed is separated by a blast of air, and a de- 

 tailed account of the method will be found in one of the bulle- 

 tins (10) of this station. In experiments carried on at the labo- 

 ratory it Vt'as found that the plants from heavy seed were less 

 liable to the trouble than the light, discarded seed ; these latter 

 did not produce strong, healthy plants, but were weak, and 

 thus more liable to the trouble when favorable conditions were 



