300 
ticularly in the middle-western, intermountain 
and Pacific Coast states. Usually this disease 
is not considered serious by alfalfa growers, 
but in many instances the writer has noted 
that the disease may be more or less disastrous 
and may produce a very decided loss in yield. 
During the last few years particular attention 
has been paid to this disease because of its 
very great prevalence in the intermountain 
states. In the Salt Lake Valley, Utah, this 
disease has been considered by many of the 
farmers as being due entirely to the smoke 
from the smelters. However, the writer has 
found it to be quite as serious in districts far 
removed from the Salt Lake Valley where soil 
and climatic conditions are the same. Because 
of the importance of the disease the writer has 
made some studies of which a preliminary re- 
port is given below. 
Reference to the literature indicates that 
very little has been done to determine the real 
eause of the disease. The earliest reference 
to the disease is that by Stewart, French and 
Wilson. These authors indicate that they be- 
lieve this disease to be due to a physiological 
disorder of some kind. The next references 
are by Reed & Crabill? and by Clinton. The 
most recent reference is by Crabill,t who be- 
lieves that white spot is due to the wounding 
of the tissue of the crowns of the plants. His 
experiments indicate that by cutting away a 
portion of the tissues the typical white spot 
was produced. The occurrence in nature, he 
believes, is due to the fact that the injury to 
the plants is produced in the late fall or 
winter because of the fact that he has only ob- 
served the disease in the early spring. The 
wounding of the plants in cultivation, he be- 
lieves permits the entrance of certain fungi 
which tend to rot the crowns and later the 
roots. Such plants, he has found, will show 
white spot in the early spring, shortly after the 
1‘“Troubles of Alfalfa in New York,’’ by F. C. 
Stewart, G. T. French and J. K. Wilson, Bulletin 
No. 305, November, 1908, New York Agricultural 
Experiment Station, Geneva, N. Y. 
2Va. Station Technical Bulletin, 2, 39, 1915. 
3 Conn. Sta. Report, Report of the Station Bo- 
tanist, 1915, 425. 
4 Phytopathology, Vol. 6, No. 1, 1916, pp. 91. 
SCIENCE 
[N. 8. Vou. XLVIIT. No. 1238 
plants have started to grow. Recently, how- 
ever, Crabill indicates (letter of April 17, 
1918) that he did not always find a crown rot 
of the affected plants and he thinks that crown 
rot may, therefore, be only a circumstance and, 
after all, not the true cause. 
In carrying out some experiments on the 
treatment of soils with various water-soluble 
substances, the writer, to his surprise, found 
that white spot suddenly appeared in a large 
number of the treated plots. Each plot covers 
an area of 25 square feet, composed of fifty 
plants from two to three years old. The plants 
have been very carefully cultivated with a hoe 
and the crowns have never been injured in 
any way. In general the white spot appeared 
within sixty to seventy hours after the soil had 
been treated. In no case did a single speci- 
men of white spot appear in the check plots. 
Furthermore, white spot did not appear in any 
of the plots where the total water-soluble sub- 
stance applied was below a certain amount. 
Further experiments indicated that the “soil 
solution ” alone would not produce white spot, 
but that the factors of soil temperature, at- 
mospheric temperature, relative humidity of 
the atmosphere and light are important. In 
other words, it requires a certain coincidence 
of these various factors at what we shall term 
the optimum before an effect was produced 
upon the plants such as would cause white 
spot to appear. 
It may be stated here that the experimental 
plants are growing in a sandy-loam soil and at 
no time previous to the experiment had white 
spot appeared. 
The work has progressed to the point where 
the writer believes that the osmotic pressure of 
the soil solution is one of the important factors 
in the production of white spot, not only under 
experimental conditions but under field con- 
ditions as well. With conditions for trans- 
piration at the optimum, lessening or prevent- 
ing endosmose, by reason of a soil solution 
having a higher osmotic effect upon the cells of 
the transpiring organs. The degree of injury 
produced will depend upon the factors enu- 
merated above, together with the time factor 
which is all important. If these factors are 
