Plant Diseases of 1901 . 
7 
the Southeast, was so great that the presence of a new apple tree 
disease was suspected. 
I visited'this section in July and collected numerous specimens? 
but no parasitic organism could be detected by laboratory investiga¬ 
tion. Later on Mr. C. H. Potter visited some of these orchards and 
made valuable observations on the soil formation. I visited the 
locality again in September in company with Dr. Headden, and as a 
result of our observations and study, together with the experience of 
the fruit growers, we arrived at the following conclusions: 
Much of the soil on the Mesa contains an excess of marl and in 
many places this substance forms a solid substratum. At the edge 
of one orchard visited the owner was digging and burning it to make 
a cement to be used in mason work. The marl in itself is, perhaps, 
not harmful to plants; in fact, when judiciously applied to land it 
acts as a liberator of plant food, but when present in excess the soil 
is infertile. This is shown by the fact that when roots penetrate the 
marl substratum they send out few or no fibrous roots. The roots 
do not usually penetrate this substratum to any extent, consequently 
the trees are often shallow-rooted in orchards where the layer of marl 
is close to the surface. The level of the lowest roots on one dying 
tree was only ten inches below the surface of the soil. At this depth 
they branched out horizontally, where they were readily injured by 
lack of moisture and by the action of frost. But a more immediate 
cause for this condition of the trees is found in the water supply. 
Water is plentiful during the early part of the season, but in the 
latter part of June the supply has usually been exhausted. The 
nature of the soil is such that it readily dries out and the trees suffer 
for moisture, consequently growth stops and the tissues harden. In 
the latter part of July a partial supply of water is again turned into 
the ditches and the orchards are irrigated. The result is that in 
many instances these trees make a distinct second growth which is 
immature when cold weather comes on. Those branches which are 
not killed outright but are severely injured during the winter put 
forth a feeble growth the following spring. The end bud, usually 
being the strongest, lives at the expense of the others, consequently 
many of the side buds soon die if they start into growth at all, and 
the terminal one develops a contracted branch on which the leaves 
are crowded, thus forming the rosette. 
Second growth is not always necessary, however, for the appear¬ 
ance of this disease. Shallow-rooted trees planted in a soil that is 
quickly dried out are easily injured during the winter. This prob¬ 
ably accounts for the fact that the disease first attracted general 
attention after the hard winter of 1898-99. 
One orchard was visited in which a small number of diseased 
branches had appeared, but which had been promptly removed or 
severely cut back early in the spring. At this date, October 5, the 
