THE MOSAIC DISEASE OP TOBACCO. 11 



Evidence at hand indicates that the species Datura metalloides L. 

 and D. leichhardtii F. Muell. may also be as resistant to the disease 

 as the species D. fastuosa. During the season of 1912 the occurrence 

 of the mosaic disease was noted in a plat of Datura species growing 

 at Arlington, Va. The relative susceptibility of these species to in- 

 fection was well illustrated in this plat. Late in the season prac- 

 tically all the plants of the species D. stramonium and D. quercifolia 

 had developed well-marked symptoms. On the other hand, the spe- 

 cies D. fastuosa, D. metalloides, and D. leichhardtii showed no 

 observable symptoms of mosaic throughout the season. 



All efforts to communicate the mosaic disease of tobacco to plants 

 of other families than the Solanaceae have always given negative 

 results. The following plants have been inoculated by the most 

 rigorous methods without any visible symptoms of the disease: 



Polygonacese — Sheep sorrel (Rumex acetosella L.). 

 Leguininosse — 



White clover (Trifolium repens L.). 



Bed clover (Trifolium pratense L.). 



Peanut (Arachis hypogea L.) 



Soy bean (Glycine Mspida Moench.). 

 Cruciferse — 



Cauliflower (Brassica oleracea L.). 



Peppergrass (Lepidium sp.). 

 Plantaginacese — Rib-grass (Plantago lanceolota L.). 

 Labiates — Dead nettle (Lamium amplexicaule L.). 

 Oxalidacese — Wood sorrel (Oxalis striata L.). 

 Composite — Garden lettuce (Lactuca saliva L.). 

 Pbytolaccaceae — Pokeweed (Phytolacca decandra L.) 



SPECIES AND SPECIES HYBRIDS OF NICOTIANA. 



A considerable number of distinct species of Nicotiana have been 

 inoculated at all stages of growth with the virus of the mosaic disease. 

 Of the various species tested all, with the exception of two or three, 

 readily became affected with the disease. It has been produced in 

 the. following species : Nicotiana silvestris, N. rustica, N. longiflora, 

 N. alata, N. plumb aginifolia, N. forgetiana, N. paniculata, and N. 

 langsdorfii. 



On the other hand, after the most persistent and rigorous methods 

 of inoculation, the species Nicotiana glauca and N. viscosum, so far 

 as observable symptoms are concerned, do not seem to be affected by 

 the disease. N. langsdorfii, which appeared to be immune, finally 

 developed the disease in one or two plants after a long series of 

 inoculations with the virus. Plants of this species when inoculated 

 through the stalk and petioles seem particularly susceptible to a very 

 destructive and progressive rot, which begins at the point of inocu- 

 lation and finally kills the plant by slowly involving the surround- 



