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Th3 lflFlUENCE OF HAHIlING SEED STOCK

 

ON

SHRINKAGE AND PIANT BEOLUCTION

 

OF THE

TRIUMPH SWEETPOTATO

 

Thesis for degree of m. 3.

William Stacy inderson
M

1956

2; a "‘1 23/937
/fl My

 

THE INFLUENCE OF HAHDIIHG SEED STOCK
ON
SHRINKAGE AND PLANT PRODUCTION
OF THE
TRIUMBE SWEETPOTATO

I N T h 0 D U C T I O N

 

Although the sweetpotato is grown extensively
in the southern portion of the United States and large
quantities are placed in storage annually, little in-
formation is available on the effect of handling on
losses of seed stock incurred from Shrinkage and decay
incident to storage, or the subsequent effect on plant
production. Undoubtedly growers could well afford to
handle their seed stock more carefully. The object
of the investigations reported herein has been to
study the eifects of "careful" handling and "commercial"
handling on the loss in weight of seed stock during
storage and on subsequent plant production.
REVIEW OF lIngATUhE

‘ Thompson and beattie (a) determined the Shrink-
age of "carefully" handled and "commercially" handled
roots of the Haney Hall and Dooley. The work was done
in five storage houses during four seasons. Tne storage
period of different seasons varied from 114 to 161 days.

These investigators found marked differences in shrink-

110610.

 

-2-

age and per cent rots between the "carefully" and
"commercially" handled lots. The average shrinkage
of the "carefully" handled lot in all of the tests
was 7.52 per cent, and of the "commercially" handled
lot 10.00 per cent. The average loss due to decay
in the "carefully" handled lot was 0.45 per cent and
in the "commercially " handled lot 3.00 per cent.

In a supplementary study, Thompson and beattie
(8) harvested roots of the Big Stem Jersey, Nancy Hall
and Southern Queen. They placed bruised roots in one
lot and non-bruised roots in another. Both lots were
then cured at 80 to 900 F. ior 15 days and stored for
164 days at a temperature varying from 50° to 55° F.
Here again Thompson inc beattie obtained marked differ-
ences in shrinkage between the bruised and non~bruised
lots. The bruised lot lost 28.13 per cent of its original
weight and the non-bruised lot lost only 15.85 per cent.
The bruised lot also had a greater per cent of decay.
These authors concluded that growers could well afford to
handle their sweetpotatoes more carefully, both in the
field and in the storage house.

Smith (7) compared the effect of "careful" and
"normal" handling on the keeping ability of Ifish potatoes.
He found that mechanical injuries to tubers incurred
during harvesting and handling have a marked influence on
the loss in weight and decay during subsequent storage.

In two experiments the "carefully" handled lots lost

 

4.46 and 5.49 per cent of their originalxweight, and the
"normally" handled lots lost 7.08 and 8.45 per cent. In
the second experiment, the amount of loss due to decay
was determined. The "carefully" handled lot had 1. 16
per cent and the "normally" handled lot 2.29 per cent
decay.

Lauritzen (4) stored small cured lots of the
Little Stem Jersey in a laboratory for a period of 17
days. He found that, though black rot may infect un-
bruised roots, as a rule the pathogene gains entrance
only through bruised tissue.

lauritzen and harter (5) found that RhiZOpus
rarely infects sweetpotatoes except through fresh wounds.
On this basis success in keeping sound sweetpotatoes in
storage, even at high humidities and in the presence of
the organism, can be satisfactorily explained. These
investigators concluded that any resistance developed
by the roots was located in the surface layers and has a
possible relation to cork formation. In later studies,
Lauritzen and harter (6) found that the time required
for infection of sweetpotatoes by RhiZOpus varied with
the amount of wounding.

Artschwager and Starrett (1), working wdth roots
of the Yellow Jersey variety, determined that sweetpotatos
heal their wounds by a suberization process of the cut
surface and subsequent develOpment of wound periderm.
They found that the course oi both processes was greatly

influenced by the temperature and the relative humidity of

the surrounding air. If these conditions are favorable,
both processes proceed rapidly, but under adverse con-
ditions they may be delayed, or even inhibited. Wound
periderm formed readily at temperatures between 710 F.

and 940 F., provided the relative humidity was sufficiently
high. At 75.5 per cent humidity and 850 F. it appeared
after the fifth day; at 82.7 per cent humidity and 85° F.
it appeared after the fourth day, and at 90 per cent
humidity and above it appeared after the second and third
days at temperatures from 850 F. to 940 F.

Hasselbring and Hawkins (2) studied the respira-
tion of the big Stem Jersey stored under commercial con-
ditions. They found that wounding markedly increased the
rate of respiration. They measured the rate of respiration
of whole and of Split roots. They found the output of
carbon dioxide at 500 C. rangedjitm 29.8 to 42.7 milligrams

per kilogram per hour with whole roots ant from 52.5 to
60.0 mifiigrams per kilogram per hour with split roots.

The ultimate effects of wounding upon loss in weight during
storage, and on the production of sprouts were not de-
termined. In the same study the authors obtained a posi-
tive correlation between reducing sugars and respiration

- rate. however, they state; "seasonal Changes in tempera-
ture and other environmental conditions to whicn the
sweetpotatoes had been subdected tended to obscure any

such correlation in difierent lots."

M TEEIAIS AUL TETBOLS

The sweetpotatoes used in this study were
grown on uniformly fertilized and cultivated Luston fine
sandy loam soil. harvesting was accomplished by plowing
out the roots with an ordinary moldboard plow. The 1934
lots were harvested on Lecember 5, and the 1955 lots on
November 12. Only roots of the size of J. 3. ho. 1 and
U. 3. ho. 2 grades were taken. Seven busnels were
handled "carefully" and seven bushels were handled "com-
mercially." "Careful" handling consisted of placing
the roots directly iron the row into crates lined with
cotton outing cloth. "Commercial" handling consisted of
throwing the roots of five acjacert rows into the center
row ind placin5 them into non-lined crates. This is the
usual way in which sweetpotatoes are handled in hississippi.
Within each lot the crates were rumbered from one to
seven, and immediately transported to the sweetpotato
storage house at the laurel Starch glint for curing and
storing.

higure l is a sketch of the floor plan of the
house. The experimental stacks were 911080 adyicent to
the inside aisles near the rear of the roomr- the "care-
fully" handlec lot at A and the "commercially" handled
lot at h.in Room 2. To permit the use of the "Student"

methoc of analysis cf the experimental data the crates of

 

 

~6-

each 1ot were placed in adjacent stacks and each crite
was placed in comparable positions in each stack. Thus,
for each lot, crate ho. l was placed on the ialse floor,
crate No. 2 above it and CTJtGS nos. 3, 4, 5, 6 and 7

in the order named with crate ho. 7 on tOp.

In 1954, the roots were cured from ie-ember 6
to 24, and in 1955 irom Lovember 12 to 24. Luring the
curing period of each geir the temperature remained fiirly
constant but the humidity varied considerably. In 1954,
the curing period temperiture ranged from ‘20 to 920 1.
and averaged 88.40 E. In 1955, it ringed iron 780 to
950 r. and averaged 90.00 r. The humidity during this
period in 1954 ringed from 25 to 70 ner cent and averaged
45.1 per cent. In l9?5, it rangee irom 56 to 82 per
cent and averaged 66 per cent.

The storage season in the 1934-2: work extended
from Lecember £4 to nirch 15. In the 1935—26 work it
extenbeo iron Lovember at to Februiry 17. Luring the
storage period oi both yeirs the tehperature within the
storage room varied consideribly. the iverage experi-
ture of the stacks was determiied by readings three times
per da‘ on thermometers pliced it the bottom, niedle and

1

tOp of the SthK . This mean tenperature varied during

U.

the storage season of 1954-55 iron 480 to 710 3. 3rd
averaged 560 F. It varied irom EOOto 7znflanc averiged
550 F. during the storige season of 1935-26. humidity,

determined by a sling psychrometer in the ai 1e Opposite

CO

the experimental stacks at the same time temperature

readings were Eide, varied iron 62 to 95 per cent and

 

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averaged 84 per cent during the storage season 01 1954~85.
It Varied iroh 61 to 94 per cent and averaged 63 per cent
during the storage season oi 1925-56. flfiort was made to
maintain high humidity by manipulation oi the vents, by
Operation oi the electric fan in the heater unit, and
by distributing shallow pans filled with water or the
floor in the aisles throughout the room.

The evaporating power of the air was measured
by means oi livingston spherical bulb atnometers. One
atmometer was placed on too oi crate ho. 7 and one on
the floor adgacert to crite to. 1. These atmometers
were weighed at weekly intervals to determine the loss
of water.

hat; on shrinkage were secured by weighing each
crate at intervals oi two weeks throughout the storage
periOd and on percentage oi rots by weighing the decayed
roots at the end oi the storige period.

Soon after the erd oi the storage perioo (on

(.1

March' 0 ior the 1925 work and on iebruary £4 ior the
1956 work) the roots oi eacn lot were weighed singly,
dipped ior 10 minutes in a 1-1000 corrosive sublimate
solution, and bedded four inches deep in a six-inch
layer oi river bed sand contained in an outdoor prOpa-
gating bed. To secure a series 0* uniiorm pairs, roots
of identical crates were sliced in adjacent plots in the
bed. ror the bed used in 1555, bcttom heat was provided

.-

by applying steam (alterrately) through both erds 01

three-inch tile lires placed 15 inches apart and 131Q 22

O - - . - . Q
1nnr.n_x noon 1+ Aha nY‘n n+ f. n “finnnnr‘ \1-1'v‘r1 Ear: :11‘!. 1M 11nr.haa

deep at the other end. Because oi the heating eifect oi
sunshine and the cooling eiiect oi rains during the early
part of the prOpagating period and despite the applica-
tion of warm water during cool weather and cool water
during warm weather, the temperature in the bed fluctuated
between 650 and 1020 E. The daily mean maximum and mini—
mum temperatures oi the bed were 900 and 73° F., respec-
tively. For prOpagation in the 1926 work a bed was con-
structed like that described by lsbell and Kimbrough (5)
for Which heat was provided by conducting the smoke irom
a pit iurnace through a six-inch air Space underneath
the floor oi the bed. A compact clay covering iour inches
thick at the iurnace end and two incnes thick at the
stack end oi the bed was placed on the iloor. The medium
(six inches 01 river bed sand) was placed on this lager
oi clay. l covering oi light muslin (which could be
raised or lowered) was provided ior the bed. a continuous
record oi the tenperature oi the bed was secured by
placing the bulb oi a soil-air thermograph within the
medium among the roots oi each lot. lespite the pro-
tection furnished by the covering and firing at regular
intervals during cool weather, the temperature oi the
bed fluctuated between 680 and 102° F. fhe dail; Kean
maximum and minimum temperatures oi the bed were 650
and 75° F., respectively.

In 1355, pulling oi the plants began on April 29

and continued at intervals of 3 to 5 dags until august 2,

-10...

when plant production had practically ceased. In 195
it began March 26 and continued until July 15, anen
plant production hid practically ceased. The plants
were pulled singly, counted and weighed collectively

for each crate.

PRESEuTATiOU Or hESULTS

 

Shrinkage. Che data on shrinkage and on per-

 

centage or rots oi individual crates and on the average
shrinkage and percentage of rots oi all crates ior the
work of 1954-55 are presented in table 1, and ior the
work 01 1955-56 in Tible a. liiierences in the Shrink-
age between the "careiully" and the "commercially"
handled lots were very striking in both years. In the
1954-55 experiments, ior the period oi Lecember 24 to
January 21, the "careiully" handled lots lost less
weight than the "commercially" handled lots in 6 cases
out 0f 7, ior the period oi January 22 to zebruary 18

in 5 cases out oi 7, and ior the periou 01 -ebruary 19
to harch 15 in 6 cases out 01 7. Thus, in 17 cases out
of 21 the "carefully" handled lOts lost less weight than
the "commercially" landled lots. fhe diiierences were
signiiicant ior the second storage period (January 22
to February 16), the third storage perioc (hebrurry 19

to Karen 15), and ior the entire storage period (hecember

24 to March 15). The; were not significant ior the Iirst

 

 

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storage period (Lecember 24 to January 21). In the
1959-36 eXperiment, nor the iirst storage perioe
(November Eb to pecember 23) the "careiully" handled
lots lost less weight than the "commercially" handled
lots in 7 cases out oi 7; ior the second storage period

(December 24 to January 20) in 6 cases out oi 7~ ior

9

‘

the third storage period (January 41 to iebruary 17)
in 4 cases out oi 7, and ior the entire storage period
(November 25 to hebruary 17) in 17 cases out oi £1.
The diiierences were signiiicant ior the iirst, second,
third, and entire storage -eiiods.

Ihe results oi both gearg' experinents also
show that, regardless or the netnoc oi handling, the
roots stored in crates t, 6 are 7 (located ir the upper
level oi the storage house) lost none weight than those
stored in crates l, S and 5 (located in the lower level
oi the storage house.) Tlia diiiererce was due, par-
tially at least, to a somewhat LiELSr evaporation in the
upper level than in the lower level, since LLB evapo-
rating power 01 the air Was higher in the upper level
than in the loner level. :-e temperature also remained

_‘

slightly higher at the urges; level than at tne lower
level. See Tables 5 and a.

The data :01 botn years als“ snow that, with
one exception :or each ;ear, the roots lost more weight

during the first and during the second period 0; storage

than during the third. The data in Tables 2 and 4 show

 

 

 

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-15-

that a somewhat higher humidity was maintained during

the third period than during the iirst and second
periods. Since irtschwager and Starrett (l) have

shown that the higher the per cent humidity the more
rapid is the develOpment Ol periderm in storage, this
greater humidity oi the third storage period undoubted-
ly induced a iaster groWLh oi periderm Which in turn
reduced the rate oi Shrinkage and the rate oi water loss.

Storage hots. Liiierences in percentage oi

 

rots between the "careiully" and "commercially" handled
lots, though not statistically signiiicant in the 1924-25
results, are rather striking. ln 5 out oi 7 cases the

"carefully" handled lots had a lower percentage of

J

storage rots than the "commercially" hantlec lots. The
data ior 1925—56 show very low percentages oi decay and
that there was no diiierence in decay between the "care-
fully" and "commercially" handled lots. Obviously,
bruising should be avoided in order to reduce to a mini-
mum the chances oi entrance oi decay organisms.

In “eneral these results.agree with those oi

r

(T

r~

Thompson and Beattie (3) and oi Smith (1). Thompson
and Beattie iound that "careiully" handled roots oi the
Looley and Nancy hall varieties oi the sweetpotato lost
less weight and had a lower percentage oi storage rots
than those "commercially" handled. Snitn iound that
"careiully" handled tubers oi the hural Russet irish

Potato lost less weight and had a lower percentage oi

storage rots than those "norna115" handled.

-17-

Plant Production. The data on plant production

 

are presented in Tables 5 and 6. These data show that
in all cases the "careiully" handled lots produced sig-
niiicantly more plants per root and per bushel than the
"commercially" handled lots. There was practicallt no
diiierence in the size oi individual plants produced by
the two lots. lppirentlg bruising the roots oi seed
stock does not iiiect the size oi sprouts. in all cases
the "careiully" handled lots required by iar less weight
oi root to produce unit weight oi plant. The "careiullg"
handled lots procuced £039 plants per bushel in 1v35
and 2615 in 1956. The "commercially" handled lots pro-
duced 1166 plants per bushel in 1955 and 1745 in 1956.
The diiierences oi 963 plants per bushel in 1925 and 668
in 1336 are highl; signiiicant.

ligure 2 illustrates the eiiect 01 handling
seed stoc? on the earliness oi sprouting. Lati presented
in Table 7 show that no sprouts were gulled ;rom the
"commercially" handled lot at the time of the iirst
pulling :rom the "careiully" handled lot. it the second
pulling iron the "careiully" nindled lots the iirst
plants were taken irom the "commerciillg" handled lots.
it all pullings the "crreiully" handled lots produced
more plants than the "commercially" handled lots. She
diiiererces between the two lots were greater at the
earl; pullings than liter in the season. Ine e results

are oi considerable importance. Shed show that "care-

(D

iully" handled seed stock CAR he xpected to sprout

Influence oi handling Seed Stock on Plant

 

 

 

 

 

 

 

 

 

 

 

 

Brocuction oi the Triumph Swectpotato, 1955.
, Treat— Mean 30. mean Grams flants
911T ment Jeight Slants Ycight EOOt per 60
hoots per root” Blant per sound 0
(Grams) (Grams) brim , bushelu
filant”
1151;1V15111 341113
1 1% 17 $5.5 12.0 4.4 2.2 1865
B 170f8.5 7.0 5.8 6.4 1120
, A 17617.0 12.8 4.9 2.8 1975
‘ B 142f8.3 5.8 4.0 6.1 1126
a 4 l9lt7.6 12.6 5.1 2.2 1805
” B 195:12.7 10.1 4.5 4.2 1411
4 1 181t7.1 14.4 5.0 2.5 2178
B 176flO.l 5.6 5.2 6.0 867
1 19118.7 18.1 4.2 2.5 2569
5 B 15759.7 5.9 5.1 5.2 1125
6 d 177:4.5 17.0 5.2 .2.0 2619
5 195214.9 7.7 4.8 5.2 1088
7 4 186:7.8 15.6 4.5 5.0 2002
B 161t14.5 9.1 4.7 5.7 1558
nan7111ixu13
1—7 A 13242.2 14.5 4.76 2.71 2129
(incl.)B 171T4.2 7.5 4.58 5.26 1166
Liiierence
(; minus 8 11:4.7 7.05* 0.14** 2.55 965*

 

*(‘fl l"? t-’

.’.
.i.

Liiierences

"Carefully" handled.

. "Commercially" handled
Based on original number 0: roots bedded.
1T8 consiterec significant.
hiiierences are considered insigniiicart.

 

-19-

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 6. Influence of Handling Seeo Stock on Plant
Production of the Triumph Sweetpotato, 1956.
Treat- Mean 80. Mean Grams Plants
Pair ment Height Bl1nts Veight Loot per 60
Boots fer root. Elant per Pound q
(Grams) (Grams) Gram a Bushelv
Plant”
111.5171 5'0 .11 13.11113
1 A} 9245.1 9.8 5.1 1.8 2899
B“ 10854.9 6.2 5.8 5.0 1557
2 A 97:5.5 9.7 4.6 2.1 2755
B 2525.6 8.2 6.5 2.5 1817
3 A 11657.1 12.0 5.1 1.8 2841
B 10055.9 7.6 5.6 2.5 2059
4 A 11556.5 11.5 5.8 1.7 2648
B 88i5.1 6.0 5.5 2.7 1845
5 A 15928.2 11.8 5.7 2.0 2297
B 56f7.1 8.1 7.1 2.5 1626
6 A 118:5.7 11.8 6.2 1.0 2728
B 14819.0? 618 6.1_ 5.6 1262
7 A 16138.5 12.7 6.5 1.9 2145
B 112t5.0 8.5 7.1 1.8 2055
1510; ii 3.183
1-7 1 11732. 11.50 5.54 1.75 2615
(incl.)B 11552.0 7.54 6.20 2.54 1745
Eifference
(1 minus B) 4i5.2** 5.96* 0.66** 0.79* 868*

 

* ()1 m H

.x.
*.

"Carefully" handled.

"Commercially" handled.
based on original number 01 roots bedded.
Lifierence considered sig111101nt.
Liiierence considered insignificant.

 

-20...

Table 7. Influence of Handling Seed Stock on Berliness oi
Sprouting of the Triumph Sweetpotato, 1956.

 

 

Pair Treat- Number plants per bushel at various pullings

 

 

 

 

 

 

 

 

 

 

 

 

ment _
1 2 5 4 5 6 7 8 9
1551v15041 81153
1 A} 557 211 509 174 290 104 118 502 174
84 0 59 154 175 117 106 158 165 80
g g 405 255 554 162 166 119 119 190 188
5 0 70 157 151 172 154 120 98 58
5 A 544 206 506 155 222 115 157 129 215
B 0 112 155 145 154 180 121 154 171
4 1 275 285 261 145 175 126 167 140 151
5 0 122 219 90 217 102 155 122 117
5 A 186 197 206 .154 165 210 151 98 157
B 0 19 67 217 156 78 117 114 141
6 4 255 215 508 202 206 182 157 148 206
b 0 22 102 65 165 56 129 112 102
7 4 109 151 244 182 125 108 126 10 207
B 0 55 117 57 109 106 168 149 200
11:5..u1 21158
177 1 269 215 284 160 192 157 129 158 185
(1561.) B 0 65 156 125 152 109 155 127 155
Difference
(1 minus 8) 269 148_ 148 55 40 28 4 51 50

 

A "Careiu115" h1ndled.

B "Commercially" hardled.

 

 

earlier and therefore produce more plants per bushel
oi seed stock ior early setting than "commercially"
handled seed stock. They indicate a Siving to the
grower in bedding space iOr production oi early plants.
The diiierence in plant production between
the tn) lots is undoubtedly associated with the dif-
ferences in the extent and the degree 01 bruising of
the two lots. 1t the eno oi the olant procuction period
a careful examination oi the roots 01 both lots re-
vealed that the bruised areas were larger and deeper
on those 01 the "commercially" handled lots than on
those oi the "cureiully" handled lots. E0 plants
were produced in the bruised areas. T he data show
that the "carefully" handled lots averaged 4.910.15
lesions per root in 1955 and 4.910.08 in 1956. The
"commercially" handled lots averaged 7U710.26 lesions

per root in 1955 and 8.630.18 in 1956. 1‘55 differ-

(D

.‘G \ . f. 1. ,. ,.
nce 1 1.755 oi 2.8-0.5 ano of 5.7f0.19 in 1956 in
iavor of the "careiully" hindled lots is considered

significant.

 

 

 

 

Figure 2. jifect of handling seed stock on plant
production. "Commercially" handled lot at leit,
"carefully" handled at right. Photographed on day 01
iirst pulling from "carefully" handled lot, Iour weeks
irom date 01 bedding.

 

S U M M A R Y

in these investigations two lots each con-
taining seven bushels of roots were harvested from a
uniform iield. One lot was handled "carefully"
during the harvest by placing the roots directly from
the row into cloth-lined crates, and the other lot
was handled "commercially" by throwing the roots into
"heap" rows and then placing them into nonlined crates.
Both lots were artificially cured at a high tempera—
ture and a moderately high humidity 17 days in 1954
and 12 days in 1955. They were then stored at a tempera-
ture of approximately 550 F. 80 days in the 1954-55
work and 84 days in the 1955-56 work. Each lot was
weighed at two week intervals to obtain the rate of
shrinkage. The decayed roots were weighed at the end
01 the storage perioa to determine the percentage of
decay. The roots of the two lots were placed in ad-
jacent positions in a propagating bed. rata were
obtained on the weight and number or plants produced.

Lats hivabeen presented wnich show, under the
conditions of these erperiments, that "carefully"
handled seed stock loses less weight and has less de-
cay in storage, and produces significantly more plants
per root and per bushel than "commercially" handled

seed stock.

-24-

These results have great practical signifi-
cance. Seed stock can be handled "carefully" by
placing the roots directly from the rows into boxes,
crates, hampers or baskets having a smooth inside
and storing in these containers at a cost actually
below the cost of "commercial" handling usually
practised. In "careiul" handling only one handling
of the roots is necessary-~that oi placing them into
the containers. In "commercial" handling they are
usually handled three times-~thrown into "heap" rows,
then placed into wagons or trucks ior hauling, and
finally placed into storage. The cost oi storage
containers would not exceed the cost or labor ior two
handlings of the roots. Even ii the cost of "careful"
handling were greater, it would pay ior itself be-
cause it resulted in a 62 per cent increase in plant
production. These results indicate a considerable
possib‘e saving to the grower irom "careful" handling
in the required storage and bedding spaces ior pro-
duction of unit quantity of plants. "Careful" hand-
ling would actually reduce the cost of production.
Consequently growers should handle their seed stock

sweetpotatoes as careiully as possible.

 

-25-

ACKNOWLEDGMEETS

 

The author gratefully acknowledges the aid
of Lr. J. B. Edmond, iormerly associate horticul-
turist, miSSiSSippi State College, who oiiered many
helpful suggestions during the progress oi the in-
vestigations and in the interpretation oi the re-
sults and preparation of the manuscript; of Lr. 3. F.
HOpkins, Biochemist, Experimental Starch Project,
laurel, mississippi, who read the manuscript; and of
Broiessor V. R. Gardner and Dr. Chas. H. Mahoney, oi
the Department of horticulture, hichigan State
College, who read the manuscript and oiiered helpful

criticisms.

 

 

1.

(\fi

8.

IITERATUEE CITED

Artschwager, E. and Starrett, R. C.

Suberization and Wound Beriderm
Bormation in Sweetpotato and
Gladiolus as Aifected by Tempera-
ture and Relative Humidity.

Jour. lgr. hes. 45:353-564, 1931

hasselbring, h. and hawkins, I. A.

Respiration Experiments with
Sweetpotatoes. J our. Agr. hes.
5:509-517, 1915.

Isbell, C. I. and Kimbrough, 7. D.

Wood constructed iire heated hot
beds for production oi sweetpotato
plants. Ala. igr. Exp. Sta. nul.
217, 1922.

Iauritzen, J. I.

Iniection and Temperature Relation
of Black hot oi Sweetpotatoes in
Storage. Jour. lgr. hes. 55:663-
676, 1926.

Iauritzen, a. I. an< harter, I. I.

The Relation oi humidity to Iniection
of Sweetpotatoes by hhiZOpus. Jour.
Agr. hes. 33:527-t59, 1926

lauritzen, a. I. and garter, I. I.

The Influence oi Temperature on
the Iniection and Lecay oi Sweet—
potatoes by hiiierent SLecies oi
hhiZOpus. Jour. igr. hes. 50:793-
810, 1925.

x

.-
a

Smith, Ora

Studies oi Botato Storage. Cornell

L

Trampson, i. C. and heattie, J. H.
Sweetpotato storage studi
o

e
f igr. Lept. Bul. 1068, 1922

 

N
_ g1? ,