778 
Journal oj Agricultural Research voi. xxiii. No. xo 
Bureaus of Plant Industry and Entomology, United States Department 
of Agriculture. 
In certain particulars the early stages of the nematode disease of wheat 
resemble the early stages of the rosette disease. In each disease there 
may be retarded development of the plants in the spring and the leaves 
may develop a dark green coloration and become very broad and thick, 
but in nematode-infested plants there is, in addition, usually a marked 
crinkling of the leaves and stems, a condition not associated with the 
rosette disease. Also, the leaf and stem tissues of nematode-infested 
plants are very vegetative and succulent in nature, and they show a 
characteristic sparkling surface. None of these characters are associated 
with the rosette disease. 
In reviewing the literature 11 it was found that certain diseases of sugar 
cane show marked resemblances in certain particulars to wheat rosette. 
The Fiji disease as described by Lyon (77) is especially similar, and like¬ 
wise the Sereh disease described by the same writer has certain charac¬ 
teristics in common with the rosette disease. 
In certain particulars the mosaic disease of cane and that of corn 
resemble the rosette disease even in the matter of leaf mottling. The 
latter character has always been observed by the writer in connection 
with wheat rosette, but since it also occurs in varieties not susceptible 
to rosette it is not known whether the condition is directly connected 
with the rosette disease. Evidence in hand suggests that there may be 
a connection. 
CAUSE OF THE DISEASE 
It should be noted that the development of typical plant symptoms of 
the rosette disease seems to be connected in some way with dormancy or 
low temperatures which occur during dormancy. When plants are not 
subjected to these conditions the characteristic plant symptoms do not 
ordinarily develop. Shortening the dormant period has given fair 
results, but until methods are perfected it will not be possible to make 
much progress by working under greenhouse conditions or by working 
in the open out of the regular season for the development of winter 
wheat. 
While a number of theories have been advanced concerning the cause of 
the rosette disease, the exact cause is still undetermined. The disease has 
been variously attributed to winter injury and to abnormal soil conditions, 
such as depleted fertility, presence of toxic or injurious substances, un¬ 
favorable soil type, and improper drainage. Animal and plant para¬ 
sites and viruses have also been considered the cause. Most of these 
possible causal agents have been tested either directly or indirectly, and 
certain conclusions have been reached. These agents are discussed under 
the general divisions (1) nonparasitic factors, (a) winter injury, (b) soil 
conditions other than parasitic; (2) parasitic factors, (a) animal, (b) 
plant; (3) viruses. 
NONPARASITIC FACTORS 
WINTER INJURY 
During the season that the rosette disease was first reported (1919) it 
was generally considered, among many farmers, that die trouble was 
caused by the abnormally mild winter of 1918-19. While there is 
11 The writer is indebted^ to Dr. C. W. Edgerton for the use of his library in connection with these 
studies. 
