588 
MICROSCOPIC OBSERVATIONS. 
By THomas TAyLor. 
During the last two years the Department has received numerous 
letters from orange-growers in Florida calling its attention to a new | 
form of disease that has appeared on their orange-trees. The branches 
become covered, more or less, with a rust-like substance which ultimately 
destroys the affected parts. 
Mr. J. H. Gates, of Pilatka, Fla., under date of November 27, 1872, 
writes to the Commissioner of Agriculture as follows: 
Inclosed are a few orange-leaves, and also an orange having a dark skin, which was 
the case with nearly half of the crop of some of our growers last season. They are 
not so much discolored this season. The coloring matter, whatever it may be, does not 
injure the quality of the fruit, but it affects its market-value. Also, please find inclosed 
three branches of an orange-tree having a rusty appearance, and in some places blis- 
tered. I have trees which have lost all their tops, apparently trom this cause. Any 
information relative to the cause or cure of this disease will be gladly received by 
myself and neighbors. 
In a second communication from the same writer, dated December 
31, 1872, further information is given in relation to the so-called rust of 
orange-trees. He says: - 
It first appeared in this section (Saint John’s River, near Pilatka) about three years 
ago. The young buds were first attacked. The diséase next spread to the young 
wood, and then gradually over the tree. We observe that the disease is more general 
on the low-lands, and it generally appears on transplanted stumps having buds from 
one to three years of age. I have not known any bearing-trees to have rust on their 
bark. Some persons in this vicinity think that the rust is caused by a worm; others 
by cocci; while others suppose that the black coloring-matter on the skin of the orange 
is silica. Any light thrown on this subject by the scientific men of your Department 
will prove of great value to us. 
The following letter received by the Department from Mr. F. L. Darcy 
will not only prove of interest to orange-cultivators, but also to those 
who desire to investigate this disease. The writer first refers to insect- 
disease as being its probable cause, then to the dark stains on oranges,. 
and lastly to the rust, so called, on the branches. 
BUENA VISTA, ORANGE MILLS PosT-OFFICE, FLA., 
January 5, 1873. 
Sir: In reference to the disease of the orange-trees I have to say that I have noticed: 
it for many years, more or less, in every orange-grove that I have visited, but never in 
such quantity as to be at all alarming. In my own groves I have not for twenty years 
observed more than three or four trees affected by it. Those were budded trees—sweet 
buds on the wild or sour orange stock. These trees were inclosed in a small fowl-yard 
about 20 feet square, boarded up 5 feet high, with a small house inclosed. The trees 
outside of the inclosure within 20 feet of the former grew well, and having been set 
out and budded at the same time of the first, were all planted in 1836, and have con- 
tinued perfectly healthy. After three years’ trial I found that the four trees within 
the inclosure were still unhealthy. Every season they threw out young, vigorous 
branches which grew till they were 6 to 8 inches long, when they would commence dying 
back from the extreme ends, and the bark in most instances would become rough and 
of a yellowish hue, while the trees from year to year remained about the same size. 
I concluded to remove the fence and house from around them. This was done three 
years ago. The trees, with one exception, are now as vigorous growers and as healthy 
as their neighbors, while the fourth is gradually improving. This disease, I think, is 
produced principally by an insect. The bark of the tree is punctured and the eggs 
deposited there. In the case of the four trees mentioned I am of opinion that they 
first became diseased from being too closely confined and not having free circulation of 
air during the heat of semmer; the great stimulating quality of the fowl-house manure: 
