I
Reprinted fro11i ·the
.TOURN,\L OF FORESTRY "Vol. 56, No. 6, June 1958
Artificial Ripening of Douglas-Fir Cones
Roy R. Silen1
Pacific Northwest Forest and Range
Experiment Station, Forest Service.
U. S. Department of Agriculture,
Portland, Oregon
Doilm,AS-FIR (Pseudotsuga men­
ziesii [Mirb.] Franco) ·seed is sel­
do.
m fully ripened on the tree be­
fore late August in the Pacific
Northwest. Since natural seed fall may begin a§ early as the last week
in that month, the cone collecting
period is often short. Lengthening
·of this period is a worthwhile goal,
for it would permit better organi­
zation of cone collection and allow
skilled personnel to collect more of
the crop. Artificial ripening of
seed in cones picked in early Aug­
ust now appears to be a distinct
possibility.
The idea that cones might be
ripened off the tree has probably
been advanced many times. Dr.
J. W. Duffield, Industrial Forestry
Association ge-n e tic i s t, has sug­
gested that squirrels, in their stor- ·
age methods, might provide condi­
tions for ripening immature cones.
The present study stems from an
exploratory study of simulated
squirrel caches in 1954 by the au­
.
thor and Richard
C. Koenig on the
H. J. Andrews Experimental For-
1Cooperators in the study were Forrest
Deffenbacher and James Hutchins of the U. S. Forest Service Nursery, Carson,
Wash., who collected and extracted the
seed. Germination tests were made at the
Cooperative Seeil Testing Laboratory,
Corvallis, Ore. William Scheuner made
observations of the seedlings as a student
project at O_regon State College. Seed
weights were <leterininecl by Peter H.
Geiger, U. S. F_orest _ S rvice.
est. Cones collected early and
stored in sandy soil were found to
have an appreciable percentage of
germinable seed. The Study
A study was . begun during the
s u m m e r of 1956 to d e t e rmine
whether seed from ill:imature cones
could be ripened artificially and-, if
so, whether the seed and seedlings
produced were normal in size alld
weight. Five cone-bearing t r e e s
ranging from 5 0 t o 100 feet tall
were chosen near the Wind River
Nursery in southwestern Washing­
ton;. cones 'vere collected from
these trees on July 11 and at 10day intervals until August 30. A
collection planned for September
10 could not be made because many
of the cones had opened and shed
their seed.
Each collection consisted of 60
cones picked from over the whole
.
crown_ of each tree. These :were
uniformly about 63°F. Peat moss
was chosen to inhibit mold develop­
ment.
3. Wet storage. Cones were
stored in hardware cloth enclosures
and immersed in 'vell-aerated wa­
ter (about 56°F.) of the fish ladder
on Tront Creek Dam, near the
Wind River Nursery. This treat­
ment was begun with the August
1 collection, whereas the. other two
treatments were begun with the
Jnly 11 collection.
The various lots were kept in
storage until September 30 in· or-.
der to allow the damp-stored cones.
to mature. Then they were stored
in air until October 11, when they
were kiln dried at 110°F. maximum
temperature.
After drying, some of the cone
scales reniained closed in some lots.
In order to eliminate any_ possibl
bias from the failure of some ,cone
lots to shed their seed uniformly,
all seed was extracted by h::\nd by
breaking the scales - apart 1where
necessary. ExcePt ·: for occ4sional
small seeds in the 'tip or bhse of
the
cone1 eyery- seed: was ext acted.
..
\
'
I
The lots · were· clcianed_ in _ a-Da-
mixed and divided into 3 lots of 20
cones, each lot to be stored sepa­
rately under 1 of 3 conditions:
1. Dry storage.
Cones were
spread on screen trays and stored in
racks in a shed that was open to
the air on all sides. Temperatures kota blower to rein9ve as mi,1ch of
the debris as possible without los­
varied between 60° and 80°F.
iu"g ·any o the seed.:- Then·; : 'ran­
2. Damp storage. Cones were
stored between layers of damp peat dom sample of 200 seeds was countmoss in po,vder boxes in a dark . ed by hand from each lot for a ger­
cellar, where temperatur· wer . ll1in.ation test.. .An additional slim_
411
JUNE 1958
ple was set aside for a later seed
.weight test.
The g'ermination test '\Vas carried
out with four 50-seed sub-samples
from each lot placed on moist river
sand in plastic dishes. Seeds were
prechilled for 2 weeks at 3°0.,
then they were germinated at alter­
nating temperatures of 20° and
30° C. for 7 . weeks. To watch for
evidence of possible abnormal de­
velopment in lots from early collec­
tions, half tbe germinated seedlings
from each lot were planted in flats
in river sand and grown in a green­
house for 5 weeks.
Finally, in order to test whether
'
or not the seed had gained weight
during storage, five kernels from
each dry-stored and damp-stored
seed Jot were decoated and dried
at 80° C. for 16 hours to obtain
ovendry weight. Weights were not
obtained for wet-stored seeds.
Germination, seedling. data, and
seed weight were tested by analysis
of variance.
During the course of the study,
supplementary examinations were
made to determine differences in
embryo development for the three
storage methods. Seeds from each
lot were dissected August 2 and
August 23.
For cones receiving normal dry
storage, '' endosperms'' (female
gametophytes plus integuments)
were usually shrunken and em­
bryos shriveled shortly after-pick­
ing. Embryos in cones receiving
wet storage seemed to be develop­
ing normally on .August 23, except
that some from the early collected
lots appeared to be slightly more
yellow than normal.
TABLE l.
GERMINATION PERCENTAGES OF _SEED FR01l[ CONES COLLEC'!'ED AT 10-DAY
INTERVALS AND STORED UNDER DRY, DAMP, AND WET CONDITIONS
Collee.tion date
Cone
July
11
July
21
1
2
3
4
5
Average
0
0
0
0
0
0
0
0
1
2
3
4
5
Average
0
0
0
0
0
0
Tree
No.
storage
method
n,y
Damp
Wet1
0
0
0
2
4
1
28
32
40
35
50
36
22
6
27
59
40
31
38
39
14
38
30
32
18
48
15
23
48
30
18
33
32
24
40
29
0
0
0
0
0
0
0
0
0
2
0
0
2
39
0,
2
0
39
0
17
0
0
0
0
0
stored lots collected before August
30 did not. The wet storage meth­
od gave· eith'er poor or no germina­
tion (Table 1 and Fig. 1.).
The low average germination
percentages over the whole study
are explained by the sampling pro­
cedure. Wormy or otherwise de­
fective cones were not culled.
(Cones from individual trees
showed insect damage ranging
from 22 percent to 41 percent of
the total.) During extraction a:lld
cleiining every seed in the cone
was recovered, whether fiat or hol­
low. A unifor1n procedure was ·nec­
essary to keep the lots strictly com­
parable for germination tests. The
fact that germination percentage
in no case exceeded 59 percent
points up the high proportion of
poor seed usually removed by se­
lective cone collection methods and
·
Results
Germination. - Germination re­
sults were very clearcut. The damp­
stored lots collected from August 1
on gave good germination (29 per­
cent or better), whereas the dry10 MILLIGRAM.S
,/
f
DAM p s oRAGE
I
,
I
•'
a;,
,'
,
,
,
,
WE' S
,
,
•/ro
DAMP STORA
,.
/
V ,<'DRY
./
,'
,.
fuRAGE
Bho
%0
DATE of CONE COLLECTION
FIG. 1.-A verage germination percentages of seed, by collection
date, from cones stored in dry, damp, and wet storage.
--0 /
2
- -
-
--
6
4
DRY STORAGE
-- --- ----
6
'
,
, .
,
,
,
I
y,,'
0
0
0
6
48
8
4
45
22
DRY WEIGHT;-PER SEED
30
%
0
0
0
0
5
0
1
Embryos continued to develop in
all damp-stored lots. Except for
the July 11 collection, embryos
were nearly equal in length to those
in freshly collected cones and
slightly lighter in color. When
examined on August 23, some de­
veloping embryos were even found
in cones from the July 11 collec­
tion. Except in some of the lots
from the July 11 collection, endo­
sperms were firm.
There were large differences be­
tween the five parents in the per­
centage of seeds containing em­
,bryos.
,•
0
0
Aug.
30
1Treatment begun with August 1 collection.
40 fiERCENT
10
0
0
Aug.
20
0
1
2
3
4
5
Average
AVERAGE GERMINATION
20
0
Aug.
10
Aug.
1
-
-
---
--
.........
STORAG
,
,
'
·:,
'0i
6ho
..
DATE of CONE COLLECTION
FIG. 2.-0ven·dry 'veight of decoated seed, by collection rlate,
for damp and dry cone storage treatments.
I
ij
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I
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412
JOURNAL OF FORESTRY
effective cleaning.in commercial op­
the numbers (few) lost to damping
eratiohs. The germination percent­
off showed no apparent relation to
ages reported here represent true
- ger111ination
capacity
of
seed without any n1echincal screen­
ing.
Seed weight.-Dry-weight com­
parison after storage of seed ker­
nels from the same collection should
Considering these results in great­
er detail, -dry cone storage gave no
or insignificant germination for col­
indicate whether or not the seeds
received nutrients from the cone
while in storage.
The dry-stored
11 to Au­
cones quickly became too dry for
10. The August 20 collection
further development, whereas the
lections made from July
gust
- date of collection.
natural
was significantly lower in germina­
30 collection
(21.7 percent compared to 36.2 per­
tion than the August
cent). However, there was consid­
erable tree-to-tree variation.
Seed
obtained from one tree on August
20 germinated better than seed col­
lected on August 30.
The germination o:f the damp­
11 was
1.3 percent for the July
stored lots collected on July
zero and
damp-stored cones stayed fresh and
green.
Kernels o:f seed from early col­
lections
weighed
placed
in damp
appreciably
storage
more
after
storage than kernels from corre­
As in the case o:f dry
storage, variation with parentag0
\Vas , evident;
some trees
showed
their highest germination in lots
1, oth­
collected as early as August
ers not until August
30, and ·son1e
at an· intermediate \late.
.lection after August
nificantly
higher
No col­
1 gave
average
a sig­
result
than others.
Wet storage resulted _in no ger­
n1ination for the collections of Au­
g·ust
l and August 10, only 0.3 per­
20, and 17.3 per­
cent for August
cent for the final collection on Au­
gust
30. At best, wet storage was
poorer than dry storage.
Seedling growth.-For the damp
treatment,
the
seedlings
showed
slight but significant differences in
growth as measured by length of
cotyledons and epicotyl.
On the
average, epicotyl length was less
17 percent (0.48 inch vs.
0.58 inch) in the August 1 collec­
by about
tion as compared with the August
30
collection.
Cotyledon
also was less by about
length
14 percent
(0.75 inch vs. 0.87 inch). The per­
centage of abnor1nal seedlings was
very small in all collections. Data
taken on relative numbers of seed­
30. Apparently the
development
is
available
in
the
cones as early as August l_ and per­
haps earlier, but the cones must be
kept moist for seed maturation tu
take place.
It appears also that oxygen lev­
els must be kept above those in
well-aerated water.
Lack of ger­
1nination under wet storage condi­
based on wetting or spraying should
can1e progressively less for later
gains from damp storage as much
collection.
age September
food necessary for continued seed
tions most likely was due to oxygen
er, a percentage not significantly
30
still green when removed from stor­
2). The average difference
in seed weig'ht was 1:4 milligrams
for the July 21 collection but be­
(Fig.
collections, as, '\vould be expected.
dry storage with the August
those· collected on July
s_ponding lots of dry-stored cones
21 collection. Thereafter, germina­
tion climbed to 30 percent or high­
different from that obtained from
30 to 40 days. For instance,
11 were
fresh until August 20, but the
scales had died by August 30.
Cones collected on August 30 were
from
This difference represents· weight
a-.
37 percent over corresponding
dry-stored lots, particularly in the
case of the July
21 collection.
An indication of nossible loss o-f
vitality resultin2· from early col­
lection i8 provided by the con1pari­
son of dry weight of damp-stored
lots collected on August
1 with that
o:f lots collected when :fully ripe on
30. This difference aver­
1.2 milligrams per seed (14
August
aged
percent)
based
'\veight on August
on
the
average
30.
purpose : to determine if seed in
cones picked early in the season
would ripen under some artificial
The storage in damp
peat moss proved to be effective
whereas neither the more drastic
wet treatn1ent nor normal dry stor­
ag-e \vas effective.
With the possibilitv o:f early cone
ro11ection established, there remains
the problen1 of finding- a commer­
cial method. Some further develop­
.ments are suggested by this study.
First, a successful method seems
the cones
fresh until the seed ripens.
The ·
cones in this study that were indi­
lings with seed coat growth restric­
vidually packed in damp peat moss
tions and abnormal stem color, and
retained
a fresh
Mold may be one o:f the obstacles
to extraction of seed from early
cone collections. In this study,_ the
earlier 'collections in damp storage
became
heavily
August
20 and October
molded
between
11.
For
this reason, considerable differences
'\vere observed in various lots dur­
ing s·eed extractions, even though
the final germination percentages
were similar. The wet-stored cones
were by far the easiest to extract
from because all the scales became
widely extended.
They showed no
mo1d even though they were some­
what sliiny "'hen removed fro1n the
30.
rrhe dry-stored cones opened uni­
The study :fulfills the immediate
to depend on keeping
be tested for possible oxygen defi­
ciencies.
fish ladder September
Discussion
treatment.
deficiencies. Any storage treatment
appearance
for
formly, but the scales
were
not
spread "\videly eno11gh for easy ex
traction. Removal of seed from the
damp-stored
lots was
even more
difficult because mold had caused
_m any of the scales to remain closed.
Later collections were not as badly
affected and the August
30 collec­
tion particularly, \vhich was still
green at time of removal from stor­
'ag·e on September
difficulty.
30, g'ave little
This points up the dis­
tinct possibility o:f eliminating such
troubles from mold. As long as the
cones remain alive they are free of
mold.
I:f they could be removed
just before the
scales
die,
mold
might be avoided, and the cones
would likely open \vithout serious
hindrance.
The second purpose o:f the study
413
JVNE 1958
was to determine whether or not
would still extend the cone collec­
would produce good nursery stock.
This is
only partially answered.
The
weight
curves
of
(Fig. 2)
mination _ for collections made on
August 1 and· rater.
the seed from early picked cones ­ tion period considerably.
oven-dry
seed
and germination
running
Storage in a
stream gave
lower ger­
mination than other methods. Nor­
Small but statistically significant
percentages
bear fur­
mal dry storage of cones in air
growth differences were found in
ther inspection. Little germination
gave no appreciable germination
(Table 1)
the 5-week-old seedlings of the lots
occurred from either dry- or damp­
for collections prior to August 20
picked on August 30 and those
stored seed until kernels averaged
and
from the lots picked earlier. Mea­
over
7 milligrams; fully matured
only about two-thirds of the ger­
surable differences in other charac­
seedlings were produced when the
mination obtained from the collec­
teristics were not found.
Insuffi­
kernels- averaged over 8 milligrams.
tion
cient seed was available to make
Criteria have been soti.ght for as­
damp-storage method is shown to
nursery tests.
even
on
this
collection
August
30.
Hence
the
in ripening the imma­
sessing the maturity of Douglas-fir
be effective
Data from the oven-dry seed ker­
seed during cone collection, such
ture cones and their seeds.
nel weights give a picture consist­
as .floatation _of cones in solvents,
ent with
cone color, or embryo size.
seedling measurements.
yielded
Seeds in the damp-stored lots,
Since
however, Were more difficult to ex­
It is interesting that reductions
none has been developed so far, the
tract due to mold on the cones.
_in
epicotyl
leveling off of the curve of average
Seedlings
growth, and dry seed weight be­
seed kernel dry weight is suggested
picked as early as August
1 were
t,veen the August 1 and August
for further investigation. as a pos­
apparently
showed
sible criterion.
slightly less cotyledon and epicotyl
cotyledon
g r -o w t h,
30 collections were 17,
14, and- 14
percent, respectively. Whether this
similarity in
growth.
Sununa;y
percentage between
from
damp-stored
normal
but
Dry:-weight measurements
of the seed kernels showed that
damp storage of cones collected on
measurements is accidental or re­
A study .to determine whether
flects a meaningful reduction in
or not Douglas-fir seed from cones
August 1
_ seedling vigor 'vill require further
picked early in the season could be
slightly under full weight.
testing for an answer.
In these measurements, the re­
lots
resulted
in
seed
only
artificially ripened was made on
The artificial ripening of seed in
cones collected _from :five trees near
immature cones by some com1_ller­
duction in seed weight and seed­
the Wind River Nursery, Carson,
cial method of damp storage ap­
ling growth was much less for the
Wash.
pears possible for Dougla.•-fir. This
August 10 collection than for the
July 11 and continued at 10-day
may greatly lengthen the period of
Aug·ust 1 collection. Hence the risk
.
of producing a lighter, less vigor­
intervals
cone collection for this species, or
September. Of three storage meth­
provide
ous seedling would be reduced by
ods tried, cones stored at al:iout 63°
cones inadvertently picked before
( ollecting after August 10, which
in damp peat moss gave full ger­
they are fully ripe.
Collections were begun on
until
seedfall
in
early
a
method
of
handling