3^ 
Journal of Agricultural Research 
Vol. XXIII, No. i 
distinguished from those of sand drown, though the two diseases may be 
confused in casual examination. In both cases the chlorosis begins at 
the tips of the leaves and on the margins, and the lower leaves are affected 
first. In extreme cases of sand drown there may be some distortion of 
the leaf margin, but ordinarily the surface is smooth and the leaf attains 
full size. In potash hunger the leaf is puckered and presents an uneven 
surface because of the difference in rate of growth of the veins and 
the leaf web. Arrested growth of the periphery causes a characteristic 
curving downward of the margin, and, particularly, the tip of the leaf. 
The farmer speaks of the leaf as being “rim bound.” Chlorosis due to 
potash hunger is promptly followed by the appearance of small dead spots 
in the affected portions of the leaf. The initial stages of this spotting are 
shown in Plate 7. As the malady progresses large areas of the leaf die, 
especially along the margins which frequently become ragged and tom. 
This condition is popularly spoken of as “rimfire.” This localized dying 
of the leaf tissue in potash hunger is an important aid in distinguishing 
the trouble from sand drown. Finally, the destruction of the green 
color of the leaf in potash hunger gives rise to a dull yellow, with a bronze 
or copper overcast, whereas sand drown results in a very light yellow or 
cream color. In severe potash hunger the green portion of the leaf shows 
a dark “muddy,” bluish green shade, while in sand drown the non- 
chlorotic portion of the leaf shows the normal green color. 
In sulphur deficiency the entire leaf, including veins and midrib, as 
w T ell as the stem of the plant, is uniformly affected, the color of the whole 
being a light shade of green. This color is frequently shown when muriate 
of potash is used instead of the sulphate as fertilizer. When both sul¬ 
phur and magnesia are deficient the entire plant becomes more distinctly 
chlorotic, the color being suggestive of that characteristic of the White 
Burley variety of tobacco as it approaches maturity. As is well known, 
a limited nitrogen supply also results in a plant with leaves of a light 
shade of green. In the disease known as frenching there is a partial 
chlorosis of the leaves, but there are also morphological changes, the size 
and especially the width of the leaf being reduced through failure of the 
leaf lamina to expand normally. In the infectious chlorosis called 
mosaic there is a characteristic mottling distributed rather uniformly 
over the leaf and appearing only in growing tissues; hence it is easily 
distinguished from sand drown. 
MAGNESIA AS A FACTOR IN PRACTICAL FERTILIZER USAGE 
It has been recognized for many years that magnesium is one of the 
indispensable elements of plant food, and Willstatter (7) has demon¬ 
strated that it is an essential constituent of chlorophyll. A considerable 
number of experiments have been made concerning the fertilizing value 
of magnesium compounds, the results of which are more or less contra¬ 
dictory. Few of these tests, however, have been so planned as to throw 
light on the present problem, and in most cases the action of magnesium 
salts has been regarded as being indirect, resulting in the liberation in the 
soil of other plant food elements ( 2 ). In pot experiments with one of 
two soil types studied, Wheeler and Hartwell ( 6 ) obtained increased 
growth of barley and rye by the use of magnesium sulphate and chlorid, 
and it is suggested that the favorable effect was due, at least in part, to a 
direct nutrient action of the magnesium. Recently A. Jacob ( 3 ) has 
called attention to favorable results obtained by the German Kali Syndi¬ 
cate in the use of potash salts containing magnesia as fertilizer for pota- 
