ALABAMA
Agricultural Experiment
Station
OF THE
Alabama Polytechnic Institute
AUBURN
A Field Method for Distinguishing
Certain Orange Stock
CIRCULAR No. 17
JULY, 1912
BY
FREDERICK A. WOLF
Plant Pathologist
Opelika, Ala.
Post Publishing Company
1912
COMMITTEE OF TRUSTEES ON EXPERIMENT STATION.
HON. R. F. KOLB ------------------------------------ Montgomery
HON. H. L. MARTIN------------------------------------------------- Ozark
HON. A. W. BELL----------------------- --------------- -- Anniston
STATION STAFF.
C. C. THACHJ President of the College.
J. F. DUGGAR, Director of Station.
DEPARTMENTAL ORGANIZATION.
AGRICULTURE:
J. F. Duggar, Agriculturist.
E. F. Cauthen, Associate.
M. F. Funchess. Assistant Professor
J. T. Williamson, Field Agent.
T. J. Hawley, Field Agent.
VETERI1NARY:
C. A. Cary, Veterinarian.
1. S. McAdory, Assistant.
CHEMISTRY:
B. B. Ross, Chemist, State Chemist.
J. T. Anderson, Chemist, Soil & Crops.
C. L. Hare, Physiological Chemist.
T. Bragg, First Assistant.
EXTENSION:
L. N. Duncan, Superintendent.*
J. B. Hobdy, Assistant.*
S. I. Bechdel, Assistant.*
J. M. Moore, Assistant.*
BOTANY:
J. S. Caidwell, Botanist.
C. S. Ridgway, Assistant.
PLANT PATHOLOGY:
F. A. Wolf, Pathologist
HORTICULTURE:
P. F. Williams, Horticulturist.
J. C. C. Price, Assistant.
H. M. Conolly, Field Agent.
ENTOMOLOGY:
W. E. Hinds, Entomologist.
W. F. Turner, Assistant.
J. A. Dew, Field Agent.
ANIMAL INDUSTRY:
Dan T. Gray, Animal Husbandman.
L. W. Summers, Assistant Professor.
L. W. Shook, Assistant.*
S. S. Jerdan, Assistant.*
A. R. Gissendanner, Assistant.
C. D. Allis, Assistant.
*In cooperation with U. S. Department of Agriculture.
A FIELD METHOD FOR DISTINGUISHING
CERTAIN ORANGE STOCK.
BY
FREDERICK A. W'OLF, Plant Pathologist.
In the warmer parts of the states bordering on the Gulf of
Mexico the planting of citrus orchards for the growing of citrus
fruits on a commercial scale is becoming more and more extensive.
This fact is strikingly manifest in the two lowermost counties of
Alabama, Baldwin and Mobile. There is growing recognition
that the climatic and edaphic conditions within this portion of the
state are very favorable for orange culture. Along with this may
be taken into account the fact that the past winter, because of its
unusual rigor, has entailed severe losses to the orchardists and
nurserymen of southern Texas. Some of them have, therefore,
moved their nursery sites to these counties. Then, too, profitable
crops of oranges have been grown in this section of our state.
All of these reasons are contributory in accounting for the yearly
increase in the planting of orange groves in Alabama.
Experimentation has shown that the Satsuma orange succeeds
best for this region but only if it has been budded or grafted on
Trifoliate stock. There is reason to believe, however, that var-
ieties other than the Satsuma as well as other citrus fruits 
can be
grown successfully in southern Atabama. It is useless to make
plantations of Satsuma trees budded on Sour orange 
stock for it
will only result in the production of an inferior tree with 
a very
inferior fruit. Attention is called to this limitation of 
the Satsuma
to Trifoliate stock in a recent circular () from the 
United States
Department of Agriculture, Bureau of Plant Industry. 
It is also
pointed out in this circular that, in 1887, Prof. Otto Penzig, (2)
*The subject matter of this circular was used as a minor 
thesis in the
Department of Phanerogamic Botany, Cornell University, 
special thanks
being due Dr. H. B. Brown, now Professor of 
Botany in the Mississippi
Agricultural and Mechanical College.
1. Swingle, W. T. The limitation of the Satsuma orange to 
Tri-
foliate orange stock. Circular of the Bureau of 
Plant Industry 46: 1-10, pl.
1. figs. 6 1909.
2. Penzig, O. Studi botanici sugli agrumi e sulle piante 
affine (con
un atlanti in folio di 58 tavole). Annali di Agricultura. 
590 pp. 1887.
88
Director of the Botanical garden at Genoa, Italy, discovered a
very evident difference between the pith of the stem of the Tri-
foliate orange and the Sour orange. This structural difference is
easily seen with the aid of the low power of a microscope. Sec-
tions of the pith of the stem of the Trifoliate orange cut longi-
tudinally show more or less imperfect transverse partitions made
up of thick walled cells, the cells being irregular in size and shape
(1. c. p. 187, pl. 13, fig. 6.) A similar section of the Sour
orange shows none of these partitions, with a tendency to all the
cells being uniform in size and arranged in rows lengthwise of
the stem.
Upon the advent of this circular certain nurserymen appealed
to the United States Department of Agriculture for help in the
'l t f#
Leaves of three species of oranges. Fig. 1, Trifoliate; fig, 2, Sour; fig. 3, Yuza.
determination of their stock. Much of this stock is grown in
their own nurseries, part of it comes from other states, and some
is imported from Japan. Some so-called Trifoliate stock was
sent to Mr. Swingle who reported that part of the material was
not 'Trifoliate nor did it seem to agree in structure with the Sour
orange. It was evident that certain nurserymen were marketing
a mixed lot of Trifoliate orange stock. In view of this fact fur-
ther inquiry was made by the writer and it was found that there
is grown in Japan an orange upon which the Satsuma is budded
which is known under the commercial name of Yuzu. The Yuzu
orange is armed with spines much as the Trifoliate but the leaves
are entirely different so that they can easily be distinguished under
89
field conditions. When, however, all the leaves have fallen, as is
the case when the trees are graded in the packing shed, determi-
nation is rendered much more difficult. An examination of the
pith of the Yuzu shows a structure somewhat similar to the Sour
orange except that the cells are not so regular in their arrangement,
and they also vary in size. This makes the Yuzu easily separable
from the Trifoliate orange. While at present it cannot be recom-
mended that Satsuma oranges be budded on Yuzu yet the matter
has been made the subject of experimentation in southern Texas
with very favorable results. The Alvin Japanese Nursery Co.,
with a branch nursery at Grand Bay, Ala., finds * that Satsuma on
Yuzu will require a longer time to bring the trees into bearing but
that that the fruits will be larger and the trees probably longer
lived than on Trifoliate stock. Since, however, a very consider-
able expense is involved in the
starting of an orange grove the
planter does not wish to experiment.
He insists on oranges budded on Tri-
foliate stock. These are known to
grow well and be profitable. It
might be noted that as a result of
subsequent observation the percent-
age of Yuzu stock among the Trifo- Fig. 4.-Pith of the Trifoliate orange
in longitudinal sections showing the thick
liate was found to be very 
small and wall~ iscell that 
makeup the imperfect
that great 
care is now 
being exercised 
cross partitions.
to prevent its importation and sale as Trifoliate stock.
This work was undertaken with the aid of Frederick W.
Mally, formerly connected with the State Department of Agri-
culture of Texas, because of the various appeals, in the spring of
1910, for help in determining the kind of nursery stock. It was
very evident from the first that it would be a physical impossibility
to examine several million trees by making sections of the pith of
the stem, and also that it would be impracticable financially.
Then, too, such an examination makes it necessary that a cut be
made which extends half way through the stem. Stock examined
in this way is not readily saleable and is in a rather impaired con-
dition even though the wound may soon heal over.
*This statement is used through the courtesy of the Alvin Japanese
Nursery Company.
90
Since one does not have the leaves by which to distinguish
species in the packing shed he must look to other parts of the
plants for characteristic differences. It was found that the roots
seem to possess characters which may be used in distinguishing
the species. These are both morphological and histological. A typi-
cal stock of Yuzu has only two large roots with a few moderately
thick smaller branches, plate 1, fig. 2, while a typical Trifoliate
stock has several large roots with numerous fibrous branches fig. 1.
After examining thousands of trees in the packing shed we are of
the opinion that, if the two species are grown under similar con-
ditions, this character may fairly safely be used in distinguishing
them. Specimens will be met with, of course, which cannot be
determined on the basis of this character. They must be made
the subject of a more detailed study.
These two species can be distinguished also, when they occur
in mixed lots, by a difference in odor.
When the cortex of the root is bruised
a strong, penetrating odor, quite disa-
greeable to many will be found to
characterize the Yuzu, while the Tri-
foliate will have a faint, much milder
odor. The attention of a consider-
able number of persons has been called
to this fact and they all agree that
Fig. 5.-Lcngitudinal section of the
they are markedly different. pith of the Sour orange. Note 
the uni-
furmity in the size of the cells, their se-
These two simple methods can rial arrangement, and the absence 
of
be supplemented 
by another 
which thick walled 
cells.
is practically as easy of application. This method is based
on anatomical differences of the species. Since such differences
are fairly constant within a given species when te plants are
grown under the same conditions of soil and moisture their 
use
can be relied upon as a scientifically accurate means for identifii-
cation. These differences show well in thin cross-sections of the
roots when examined under the low power of a microscope. By
this means the differences are made so prominent that, when once
they are fixed in mind, a worker, using a hand lens, may be cer-
tain of his determination of species.
Since a microscope is not always available, and some little
skill is required in cutting suitably thin sections, some have been
cut and photographs made of these sections as they would appear
91
when seen through a microscope. For this purpose one-year old
roots about 4mm. in diameter (two-thirds the diameter of an or-
dinary lead pencil) were embedded in celloidin, sectioned and
stained with safranin and Delafield's haematoxylin. Safranin
stains red the lignified parts (wood fibers, vessels, and groups of
bast fibers) and the suberized or corky parts of the outer bark.
The medullary rays, cambial regicn, and the remainder of the
bark are stained blue by Delafield's haematoxylin. Microphoto-
graphs were then made of sectors of such sections. (Plate 11).
In each case the tissues extending from the pith area or central
area (no pith cells are present) to the outer bark are shown. In
Fig. 3, which shows a portion of the root of Trifoliate orange,
there is a rather large pith area made up of large cells. The xylem
or wood contains numerous vessels, some of w hich are very large
in diameter. These occur either singly or in groups of two to six.
The cambium forms a sharp line of
demarcation between the wood and
the bark. Within the bark are three
or four rows of groups of bast fibers,
forming broken concentric rings.
These groups are separated by rela-
tively small distances, in the two inner
rows, and are much more scattered in
the outer rows. In all of the micro-
Fig. 6.--Pith of the Yuzu orange in
longitudinal sections. Compare it with photographs the groups of bast fibers
the sour orange, noting the lack of uni-
formity in size and in arrangement of show as dark areas within the bark.
the cells.
Fig. 4 represents a similar sector of the
root of the Yuzu orange. The pith area is essentially of the same size
a- in the Trifoliate orange, but the cells are larger in diameter. The
vessels in the wood are not nearly so large and prominent, neither
is there so evident a line of separation between the wood. and the
bark. Only a few scattered groups of bast fibers are present.
This species is easily distinguished from the Trifoliate orange on
account of the smaller diameter of the vessels in the wood. Fig. 5
is a similar sector of the root of the Sour orange. The pith 
area
is so very small that the medullary rays almost converge at the cen-
ter. The vessels are comparable in size with those of the Yuzu.
The wood and the bark are quite sharply delimited. The groups
of bast fibers are close together in the inner row, and there 
are
only a few scattered groups farther out. This is a condition inter-
mediate between the Trifoliate and the Yuzu.
92
The position of the elements that are used in this anatomical
diagnosis as seen in an entire cross section, the relative sizes of
the pith areas and vessels, and the number and the distribution of
the groups of bast fibers, are represented in a diagrammatic way in
Plate III. Fig 6 is a diagram of Trifoliate orange, Fig. 7 of Yuzu
and Fig. 8 of Sour. In each sketch (a) represents the outer bark
or corky tissue, (b) one of the groups of bast fibers, (c) a vessel
of the wood, (a) the cambial or growing zone, (e) a meditilary
ray, and (f) he pith area.
When one has familiarized himself with the points of differ-
ence in structure of the roots of these three species of oranges they
can be distinguished with certainty with the aid of a hand lens. Tech-
nically trained experts are not necessary for carrying out the work.
The accuracy and efficiency of this method of separation based en-
tirely on anatomical differences has been demonstrated in our field
work. Two men working together, one provided with a sharp
budding knife with which to make a smooth, clean cut and the
other with a hand lens, can easily determine from five to six
thousand trees per day. Since it is necessary to grade all the trees
in the packing shed, the determination may be made at the same
time and need involve but little additional expenditure of time.
As a result of the field tests, one need feel no hesitancy in stating
that this method may be quickly learned and accurately employed
by the nurserymen and growers.
As is well known the difference in species of plants do not
always lend thems Ives as well to verbal description as to observa-
tion, both to the layman and to the scientist. When once the
type has been fixed in mind, however, it has relatively clear-cut,
well-defined characters. These characters may appear more and
more distinctive to the mind of the observer as a larger number of
individual plants comes under his observation. This is markedly
true in the case of the three species of oranges which have been
considered.
EXPLANATION OF PLATES.
PLATE I.
Fig. 1-Root of Trifoliate orange showing the type of branching.
Fig. 2-Root of the Yuzu orange showing the type of branching.
PLATE II.
Figs. 3-4-5.-Microphotographs of sectors of orange roots, Trifoliate,
Yuza and Sour, respectively.
PLATE III.
Diagrams representing the arrangement of parts in entire cross sections
of the roots of the three species of oranges: Fig 6 of the Trifoliate, Fig. 7 of
the Yuzu and Fig. 8 of the Sour. In each case (a) represents the corky
portion of the outer bark, (b) a group of bast fibers, (c) a xylem vessel, (d)
the cambium, (e) a medullary ray, (f) the central area.
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