ALLARD: MOSAIC DISEASE OF TOBACCO 439 
in Connecticut presented a careful account of the mosaic or 
“calico” disease as it occurs around Hartford, Connecticut, 
together with a summary of work done by foreign investigaters 
up to that time. He concluded that ‘mottled-top” was a less 
pronounced phase of ‘‘calico’’ developing in nearly mature plants. 
He likewise proved conclusively by growing seedlings from the 
seed of calicoed plants that the disease is not transmitted through 
the seed. From his extended observations in the Connecticut 
Valley, Sturgis found that calico was very sporadic in its occur- 
rence and that it could not be attributed to parasitic fungi, 
nematodes, insects, mechanical injury of the roots, cultivation, 
etc. He was finally led to believe that the disease was purely 
physiological, as the following paragraphs of his summary indicate: 
(2) ‘The disease occurs abundantly in some localities, notably 
on the close, clayey soils on the east side of the Connecticut 
River; sparingly in other localities, where the soil is open and 
porous. 
(7) “It seems probable that the disease is purely a physio- 
logical one, caused primarily by sudden changes of atmospheric 
conditions which disturb the normal balance between evaporation 
of water from the leaves and its absorption by the roots, and 
secondarily by soil conditions which prevent the speedy restoration 
of that balance. This supposition is supported by numerous 
facts.”’ 
In 1899 Sturgis (17) published the results of various liming and 
shading experiments as a preventive of calico, and as additional 
proof of the supposed physiological origin of the disease. In this 
paper he concludes “that shading may reduce the amount of 
calico, there seems good reason to believe’’; and, with respect to 
liming the soil, ‘‘that the use of lime may not, in all cases, exercise 
the deleterious effect on tobacco that some growers suppose it to, 
and that there is some reason for thinking that its use may tend to 
decrease the prevalence of calico.” 
As already shown, Beijerinck (10), in somewhat uncertain 
terms, seemed inclined to place the inciting cause of the disease 
somewhere between parasitic and non-parasitic agencies. Sturgis 
(17) completed the step and was the first to regard the disease as a 
purely physiological response to particular soil and climatic factors. 
