The Juglandaceae comprise roughly 40 tree species within six genera which provide edible nuts. The fruits are usually drupes containing a large seed (nut). Seed storage behaviour is orthodox, at least in the genera Carya and Juglans, despite many previous comments to the contrary.
SEED DORMANCY AND GERMINATION
The seeds can exhibit dormancy, which varies considerably between accessions from only slight to very pronounced. Pre-chilling, sometimes for long durations, is the usual treatment applied to promote seed germination. Detailed information is provided in this chapter for the genera Carya (including synonyms within Hicoria and Juglans) and Juglans (including synonyms within Wallia).
CARYA
|
C. aquatica (Michx.f.) Nutt. [Hicoria aquatica
(Michx.f.) Britt.] |
water hickory, bitter pecan, swamp hickory |
|
C. cordiformis (Wangh.) K. Koch. [C. amara
Nutt.; Hicoria cordiformis (Wagh.) Britt.; |
bitternut, bitternut hickory, swamp |
|
Hicoria minima (Marsh.) Britt.; Juglans
cordiformis Wangh.] |
hickory, pignut |
|
C. glabra (Mill.) Sweet [C. ovalis (Wangh.)
Sarg.; Hicoria glabra (Mill.) Britt.] |
pignut hickory, oval pignut hickory, pignut, red
hickory |
|
C. illinoiensis (Wangh.) K. Koch. [C.
olivaeformis Nutt.; C. pecan Engler & Graebn. not Nott.;
Hicoria pecan (Marsh.) Britt.; Juglans illinoensis Wangh.] |
pecan, sweet pecan |
|
C. l aciniosa (Michx.f.) Loud. [C. sulcata
Nutt.; Hicoria laciosa (Michx.f.) Sarg.; |
big or bottom shellbark hickory, bigleaf |
|
Hicoria acuminata Dipp.; Juglans laciosa
Michx.f.] |
shagbark hickory, kingnut |
|
C. myristicaeformis (Michx.f.) Nutt. [Hicoria
myristicaeformis (Michx.f.) Britt.] |
nutmeg hickory, bitter water hickory, swamp hickory |
|
C. ovata (Mill.) K. Koch. [C. alba Nutt.;
Hicoria ovata Britt.; Juglans ovata Mill.] |
shagbark hickory, little shellbark hickory, scalybark hickory,
southern shagbark hickory |
|
C. tomentosa Nutt. [C. alba K. Koch. not Nutt.;
Hicoria alba Britt.; Juglans tomentosa Poir.] |
mockernut hickory, big-b ud hickory, white- heart hickory,
bullnut, hognut, mockernut |
I. Evidence of dormancy
Despite comments to the contrary Carya spp. have orthodox seed storage characteristics (10), which means that they can be stored at low moisture contents, e.g. 5% (4), and low temperatures (4,8). Viviparous germination can occur in pecan (25) - suggesting that lack of dormancy might be more of a problem than dormancy. Dormancy can be present, however: it appears to be more pronounced in C. aquatica, C. cordiformis, C. glabra, C. laciniosa, C. myristicaeformis, C. ovata and C. tomentosa (4,5,7) than in the cultivated C. illinoensis. It is reported that varieties of the latter species which have originated from the Southern United States show no or only slight dormancy, whereas those which have originated from the Northern United States can show considerable dormancy (16,17). Even with apparently non-dormant seed lots pecan germination can be delayed with only low proportions of the seeds germinating (6,12,16,17,19,23,24,27,30,31).
II. Germination regimes for non-dormant seeds
C. aquatica
Alternating temperatures: 21°/27°-32°C (night/day), 63d, in soil (5)
C. cordiformis
Alternating temperatures: 20°/30°C (night/day), 250d, in sand, peat, or soil (1,5)
C. glabra
Alternating temperatures: 20°/30°C (night/day), 30-45d, in sand, peat, or soil (1,5)
C. illinoensis
TP: 20°/30°C (16h/8h): 28d (AOSA)
Constant temperatures: 27°C (16,17); 30°C (6,8,14,27,28,29,31)
Alternating temperatures: 20°/30°C (night/day), 45-60d, in sand or peat, or between papers (1,5)
C. laciniosa
Alternating temperatures: 20°/30°C (night/day), 45-60d, in sand, peat, or soil (1,5)
C. myristicaeformis
Alternating temperatures: 20°/30°C (night/day), 60d, between papers (5)
C. ovata
TP: 20°/30°C (16h/8h): 28d (AOSA)
Alternating temperatures: 20°/30°C (night/day), 45-60d, between papers (1,5)
C. tomentosa
Alternating temperatures: 20°/30°C (night/day), 93d, in sand, peat, or soil (1,5)
III. Unsuccessful dormancy-breaking treatments
C. illinoensis
Pre-soak: (18); hot, 2,5 min (18)
Pre-wash: 3-12d (27)
X-rays: 50 kv, 10mA, 80 min (26)
Benzylaminopurine: pre-applied, 24th, 300 ppm (12)
Ammonium hydroxide: pre-applied, 1-10 min (18)
Ammonium sulphate: pre-applied (18)
Calcium phosphate: pre-applied (18)
Calcium nitrate: pre-applied (18)
Potassium chloride: pre-applied (18)
Potassium sulphate: pre-applied (18)
Sodium nitrate: pre-applied (18)
Sodium hydroxide: pre-applied, 1-10 min (18)
Sugar: pre-applied (18)
Ether: fumigate dry or imbibed seed (18)
Chloroform: fumigate dry or imbibed seed (18)
Nitric acid: fumigate dry or imbibed seed (18)
Scarification: concentrated sulphuric acid, 10s-3 min (2); sulphuric acid, 20s (18)
C. ovata
Removal of seed covering structures: part of shell (7)
IV. Partly-successful dormancy-breaking treatments
C. aquatica
Pre-chill: 0°-3°C, 90-150d, germinate at 20°/30°C (night/day) (1)
C. cordiformis
Pre-chill: 0°-7°C, 90-120d, germinate at 20°/30°C (night/day) (1); 0°-5°C, 90d, germinate at 20°/30°C (night/day) (5)
C. glabra
Pre-chill: 0°-5°C, 90-120d, germinate at 21°/27°C (night/day) (5)
C. illinoensis
Constant temperatures: 20°C (6,8,27,29,31); 25°C (27,29,31)
Pre-chill: 3°C, 30d, germinate at 20°/30°C (night/day) (4); 0°-5°C, 30d, germinate at 21°/32°C (night/day) (5); 4°C, 90d, germinate at 20°C (8); 3°-5°C, 2,4w (19); 0°-2°C (26); 4.5°C, 17, 100d, germinate at 20°C, 25°C (31); 0°-5°C, 30-90d, germinate at 20°/30°C (night/day) (5); 4°C, 30d, then benzylaminopurine, pre-applied, 24h, 300 ppm (12); 3°-7°C, 6w, then pre-soak, 5d (13); 3°-5°C, 2,4w, then GA3, pre-applied, 24h, 100, 200 ppm (19)
Warm stratification: 6w, then pre-soak, 5d (13); 6w, then GA3, pre-applied, 5d, 1000 ppm (13)
Pre-soak: 0.5-4d (30); 1d (12); 5d (13); 7d (25)
GA3: pre-applied, 1d, 1000 ppm (12); pre-applied, 5d, 1000 ppm (13); pre-applied, 1d, 100, 200 ppm (19); co-applied, 1-1000 ppm, at 20°C (8)
Kinetin: co-applied, 1-50 ppm, at 20°C (8)
Ammonium hydroxide: pre-applied, 10-20s (18); fumigate, 1-4d (18)
Sodium hydroxide: pre-applied, 10-20s (18)
C. laciniosa
Pre-chill: 0°-5°C, 90-120d, germinate at 20°/30°C (night/day) (5)
C. myristicaeformis
Pre-chill: 0°-5°C, 60-120d, germinate at 20°/30°C (night/day), in light, 8h/d (5)
C. ovata
Constant temperatures: 17°-35°C (7)
Pre-chill: 3°C, 10°C, 1-5m (3); 3°C, 30d (4); 0°-5°C, 90-150d, germinate at 20°/30°C (night/day) in light, 8h/d (5)
C. tomentosa
Pre-chill: 0°-5°C, 90-150d, germinate at 20°/30°C (night/day) (1,5)
V. Successful dormancy-breaking treatments
C. aquatica
Pre-chill: 0°-5°C, 30-90d, germinate at 21°/27°-32°C (night/day) (5)
C. cordiformis
Pre-chill: 3°-5°C, 13w (10)
C. glabra
Pre-chill: 0°-7°C, 90-120d, germinate at 20°/30°C (night/day) (1)
C. illinoensis
Pre-chill (AOSA)
Constant temperatures: 30°C (6,8,14,27,28,29,31); 35°C (27,28,29)
Pre-chill: (2,9,18,21);1°-5°C, 30-60d (32); 3°C, 60-120d (4); 4°C, 60-90d (6); 2°-3°C, 8-20w (15); 0°-2°C, 2-12w, germinate at 27°C (16,17); 5°C, 1-14w (20); 7.5°C, 1-10w (22); 4°C, 3m (29); 4.5°C, 17,100d, germinate at 30°C (31); 3°-7°C, 30-90d, germinate at 20°/30°C (night/day) (1); 4°C, 30d, then pre-soak, 24h, germinate at 30°C, in light, 120 mol m-2 s-1, 15h/d (12); 4°C, 30d, then GA3 pre-applied, 24h, 1000 ppm, germinate at 30°C, in light, 120 mol m-2 s-1, 15h/d (12); 3°-7°C, 6w, then GA3, pre-applied, 5d, 1000 ppm (13)
Pre-soak: (20); 2-3d (16); 4-5d (11,14); 4-15d (2); 8d (30); 1w, then pre-chill, 0°-7°C, then germinate at 27°C, in light, 15h/d (25)
GA3: pre-applied, 0.5-8d, 50-5000 ppm (30)
Oxygen: 100%, 5 min/d flush, germinate at 30°C (27)
Removal of seed covering structures: shell (23,24,27); break shell (23,24,27); excise embryo (27-29)
Scarification: concentrated sodium hydroxide, 2-4 min (2); concentrated ammonium hydroxide, 2 min (2)
Ammonia: fumigation, 1-3d (2)
C. ovata
Pre-chill (AOSA)
Pre-chill: 3°-7°C, 90-150d, germinate at 20°/30°C (night/day) (1); 3°C, 60-150d (4)
VI. Comment
Pecan seed germination and dormancy have been reviewed recently elsewhere (9). Not only is pre-chilling at 3°-5°C an effective dormancy breaking treatment for seeds of Carya spp., but it is also reported to result in the prompt germination of apparently non-dormant seeds when subsequently transferred to a higher temperature for germination (6,13,15,16,17,20,22). The AOSA recommended pre-chilling treatments for C. illinoensis and C. ovata are 60 days at 3° to 5°C.
An alternating temperature regime of 20°/30°C has usually been provided for germination. High constant temperatures, 30°-35°C, may also promote full germination for seeds of C. illinoensis and C. ovata provided that the test is continued for a long enough period (7,8,14,27,28,29,31). Pre-application of gibberellins after pre-chilling can provide a further promotion of germination (12,13,19).
It is suggested that gene banks test seed of Carya spp. for germination at an alternating temperature of 20°/30°C (16h/8h) or at a constant temperature of 30°C for at least 28 days after first pre-chilling the seeds at 30°-5°C for: 30-60 days for C. illinoensis; 30-90 days for C. aquatica; 60-120 days for C. myristicaeformis; 90-120 days for C. cordiformis, C. glabra and C. laciniosa; or 90-150 days for C. ovata and C. tomentosa. Where these treatments are insufficient to promote full germination try a 1 to 5 day pre-application of GA3 at 100-1000 ppm.
VII. References
1. Anonymous (1948). Carya Nutt. Hickory. In Woody-plant Seed Manual, pp. 109-111, USDA Forest Service, Miscellaneous Publication No. 654.
2. Bailey, J.E. and Woodroof, J.G. (1932). Propagation of pecans. Georgia Agricultural Experiment Station, Bulletin 172, 4-19.
3. Barton, L.V. (1936). Seedling production in Carya ovata (Mill.) K.Koch, Juglans cinera L., and Juglans nigra L. Contributions from the Boyce Thompson Institute, 8, 1-5.
4. Bonner, F.T. (1976). Storage and stratification recommendations for pecan and shagbark hickory. UDSA Forest Service, Tree Planter's Notes, 27, 3-5.
5. Bonner, F.T. and Maisenhelder, L.C. (1974). Carya Nutt. Hickory. In Seeds of woody plants in the United States, pp. 269-272, USDA Agriculture Handbook 450.
6. Caminada, P. (1979). Germination of the pecan nut. Zimbabwe Rhodesia Agricultural Journal, 76, 237-238.
7. Crocker, W., Thornton, N.C. and Schroeder, E.M. (1946). Internal pressure necessary to break shells of nuts and the role of the shells in delayed germination. Contributions from the Boyce Thompson Institute, 14, 173-201.
8. Dimalla, G.G. and Van Staden, J. (1977). The effect of temperature on the germination and endogenous cytokinin and gibberellin levels of pecan nut. Zeitschrift für Pflanzenphysiologie, 82, 274-280.
9. Dimalla, G.G. and Van Staden, J. (1978). Pecan nut germination - a review for the nursery industry. Scientia Horticulturae, 8, 1-9
10. Gordon, A.G. and Rowe, D.C.F. (1982). Seed Manual for Ornamental Trees and Shrubs, Forestry Commission Bulletin 59, 132 pp. HMSO, London.
11. Impey, R.L. (1971). Pecan nut propagation and nursery practices. Citrus and Sub-Tropical Fruit Journal, 451, 29-30.
12. Knox, C.A. and Smith, R.H. (1981). A method for rapid seed germination of pecan. Pecan Quarterly, 15, 23-24.
13. Laiche, A.J. (1976). Growth evaluation studies of one year pecan seedlings of selected varieties, seed treatments and growing methods. Pecan South, 3, 358-361, 382.
14. Madden, G., Brison, F.R. and McDaniel, J.C. (1969). Pecans. In Handbook of North American Nut Trees (ed. R.A. Jaynes), pp. 163, 180. Northern Nut Growers Association, Knoxville, Tennessee.
15. Madden, G., Roberts, D. and Campbell, D. (1977). Stratification and chilling. Pecan Quarterly, 11, 9-10.
16. Madden, G.D. and Tisdale, H.W. (1975). Effects of chilling and stratification on nut germination of northern and southern pecan cultivars. HortScience, 10, 259-260.
17. Madden, G.D. and Tisdale, H.W. (1975). Study examines chilling on pecan germination. Pecan Quarterly, 9, 16-17.
18. McHatton, T.H. and Woodroof, J.G. (1927). Some factors influencing pecan germination. Proceedings of the American Society for Horticultural Science, 24, 125-129.
19. Nasr, T.A. and Hassan, E.M. (1975). Effect of duration of after-ripening and gibberellic acid on germination of seeds and growth of seedlings of pecan in Egypt. Scientia Horticulturae, 3, 217-221.
20. O'Barr, R.D. (1976). Germination study and seedling performancy. Pecan South, 3, 424-427.
21. Pammel, L.H. and King, C.M. (1921). Studies in the germination of some woody plants. Proceedings of the Iowa Academy of Sciences, 28, 273-282.
22. Sparks, D., Chapman, J.W. and Lockwood, D.W. (1974). Stratification promotes germination. Pecan Quarterly, 8, 13.
23. Sparks, D. and Pokorny, F.A. (1967). Effect of the shell on germination of pecan nuts Carya illinoensis, Koch cv. Stuart. HortScience, 2, 145-146.
24. Sparks, D. and Pokorny, F.A. (1967). Germination of Stuart pecan nuts as affected by mechanical scarification and shell removal. Proceedings of the South Eastern Pecan Growers Association, 63, 73-76.
25. Tedders, W.L. Calcote, V.R. and Payne, J.A. (1970). A method for rapid germination of pecan seed. Pecan Quarterly, 4, 11.
26. Traub, H.P. and Muller, H.J. (1934). x-ray dosage in relation to germination of pecan nuts. Botanical Gazette, 95, 702-706.
27. Van Staden, J. and Dimalla, G.G. (1976). Regulation of germination of pecan, Carya illinoensis. Zeitschrift für Pflanzenphysiologie, 78, 66-75.
28. Van Staden, J. and Dimalla, G.G. (1977). High temperature incubation increases germination. Pecan Quarterly, 11, 14-15.
29. Van Staden, J., Wolstenholme, B.N. and Dimalla, G.G. (1976). Effect of temperature on pecan seed germination. HortScience, 11, 261-262.
30. Wiggans, S.C. and Martin, L.W. (1961). The effect of gibberellic acid on germination and seedling growth of pecans. Proceedings of the American Society for Horticultural Science, 77, 295-300.
31. Wolstenholme, B.W. (1974). Effect of stratification and temperature on germination of pecan nuts. Citrus and Sub-Tropical Fruit Journal, 489, 9-10.
32. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
JUGLANS
|
J. ailantifolia Carr. [J. sieboldiana Maxim.;
J. cordiformia var ailantifolia (Carr.) Rehd.] |
siebold walnut |
|
J. californica S. Wats. |
California walnut |
|
J. cinera L. (Wallia cinerea (L.)
Alef.] |
butternut, oilnut, white walnut |
|
J. hindsii Jeps. [J. californica var
hindsii Jeps.] |
Hinds walnut, Hinds black walnut |
|
J. honorei |
|
|
J. major (Torr.) Heller [J. rupestris Engelm.
var major Torr.] |
Arizona walnut, Arizona black walnut |
|
J. microcarpa Berlandier [J. nana Engelm.; J.
rupestris Engelm. ex Torr.] |
little walnut, Texas black walnut, nogal, river
walnut |
|
J. nigra L. [Wallia nigra (L.) Alef.] |
black walnut |
|
J. pyriformis |
|
|
J. regia L. |
Persian walnut, English walnut |
I. Evidence of dormancy
Seeds of all Juglans spp., which - despite some doubt in the literature - do show orthodox seed storage characteristics (9), can show pronounced dormancy (1,4,6,15).
II. Germination regimes for non-dormant seeds
J. cinera
Alternating temperatures: 20°/30°C (night/day), in sand, peat or soil, in light (4)
J. hindsii
Alternating temperatures: 20°/30°C (night/day), in sand, peat or soil (1,4)
J. major
Alternating temperatures: 20°/30°C (night/day), in sand, peat or soil, in light (4)
J. microcarpa
Alternating temperatures: 20°/30°C (night/day), in sand, peat or soil (4)
J. nigra
Alternating temperatures: 20°/30°C (night/day), in sand, peat or soil in light (1,4)
J. regia
Alternating temperatures: 20°/30°C (night/day), in sand, peat or soil (1,4)
III. Unsuccessful dormancy-breaking treatments
J. nigra
Warm stratification: 20°C, 45d (7)
GA3: co-applied, 50-400 ppm (5)
Cycocel: co-applied, up to 1000 ppm (5)
Pre-soak: 5d (6)
IV. Partly-successful dormancy-breaking treatments
J. ailantifolia
Pre-soak: 10d (4)
J. californica
Pre-chill: (1); 1°-5°C, 156d (4); 1°-3°C, 5-6m (14)
J. cinera
Pre-chill: 3°-7°C, 90-120d (1); 3°C, 10°C, 4m (3); 1°-5°C, 90-120d (4); 1°-3°C, 5-6m (14)
Warm stratification: 60d, then pre-chill, 3°-7°C, 90-120d (1)
Removal of seed covering structures: part of shell over radicle, germinate at 20°C, 25°C (7)
J. hindsii
Pre-chill: (1); 1°-5°C, 156d (4); 1°-3°C, 5-6m (14)
J. honorei
Pre-chill: 1°-3°C, 5-6m (14)
J. major
Pre-chill: 5°-7°C, 90d (1); 1°-5°C, 120-190d (4)
J. microcarpa
Pre-chill: 1°-5°C, 190d (4); 1°-3°C, 5-6m (14)
J. nigra
Pre-chill; (6,12); 3°-10°C, 60-120d (1); 0°C, 10°C, 5m (3); 1°-5°C, 90-120d (4); 3°-5°C, 7°-10°C, 4m (6); 6°C, 15-100d (7); 1°-3°C, 5-6m (14)
Warm stratification: 19°-24°C, 4m (6); 20°C, 90d (7); 20°C, 45,90d, then pre-chill, 6°C, 15-100d (7)
Ethrel: co-applied, 100 ppm (5)
J. pyriformis
Pre-chill: 1°-3°C, 5-6m (14)
J. regia
Pre-chill: 5°C, 30-60d (1); 0°C, 1-6w (11); 1°-3°C, 5-6m (14)
Ethrel: pre-applied, 24h, 500-1500 ppm (16)
Thiourea: pre-applied, 24h, 500-1500 ppm (16)
Pre-soak: imbibe under vacuum (10)
Juglans spp.
Alternating temperatures: 5°/15°C, 15°/25°C (2)
Pre-wash: 7d (13)
V. Successful dormancy-breaking treatments
J. ailantifolia
Pre-chill: 1°-3°C, 5-6m (14)
J. cinera
Pre-chill: 3°C, 10°C, 2m (3)
Removal of seed covering structures: part of shell over radicle, germinate at 30°C, 35°C (7)
J. major
Pre-chill: 1°-3°C, 5-6m (14)
J. nigra
Constant temperatures: 15°C (7)
Pre-chill: 1°-5°C, 12-20w (9); 3°C, 10°C, 1-4m (3); 3°-5°C, 90-120d (17)
Warm stratification: 21°C, 1-2m, then pre-chill, 3°C, 10°C, 2m (3)
Removal of seed covering structures: part of shell over radicle, germinate at 6°-28°C (7)
J. regia
Pre-chill: 1°-5°C, 30-156d (4); 1°-5°C, 12-20w (9); 2°C, 6-8w (8); 0°C, 7,8w (11)
Juglans spp.
Pre-chill: 3°-5°C, 100-110d (13)
VI. Comment
Prolonged pre-chill treatments are required for breaking seed dormancy in Juglans spp. (1,3,4,6,7,9,14,17), whilst the removal of a small part of the shell over the radicle promotes prompt germination (7). Husks should be removed from the fruits before they dry (9). It is suggested that pre-chill treatments will be required for virtually all accessions of Juglans spp. maintained in gene banks. For most accessions 5 months pre-chilling at 3°-5°C may be required, but for accessions of J. nigra and J. regia 3 months pre-chilling may be satisfactory. Subsequent germination tests should be carried out in an alternating temperature regime of 20°/30°C (16h/8h) either on moist sand or between paper towels; the removal of a small part of the shell from the imbibed, pre-chilled, seeds may reduce the time taken to germinate.
VII. References
1. Anonymous (1948). Juglans L. Walnut. In Woody-Plant Seed Manual, pp. 201-204, USDA Forest Service, Miscellaneous Publication No. 654.
2. Baillon, H. (1882). Germination of walnut and almond. Botanical Gazette, 7, 91-92.
3. Barton, L.V. (1936). Seedling production in Carya ovata (Mill.) K.Koch., Juglans cinerea L., and Juglans nigra L. Contributions from the Boyce Thompson Institute, 8, 1-5.
4. Brinkman, K.A. (1974). Juglans L. Walnut. In Seeds of Woody-plants in the United States, pp. 454-459. United States Department of Agriculture, Agriculture Handbook No. 450.
5. Casini, E. and Salvadori, S. (1975/1976). [Observations and research on the use of various growth regulators in the germination of seeds of fruit trees.] La Nuova A.O.P.I., Dicembre 1975/Giugno 1976, 22pp. (From Horticultural Abstracts, 1977, 47, 12022.)
6. Chase, S.B. (1947). Eastern black walnut germination and seedbed studies. Journal of Forestry, 45, 661-668.
7. Crocker, W., Thornton, N.C. and Schroeder, E.M. (1946). Internal pressure cessary to break shell of nuts and the role of shells in delayed germination. Contributions from the Boyce Thompson Institute, 14, 173-202.
8. Forde, H.I. (1975). Walnuts. In Advances in Fruit Breeding (eds. J. Janick and J.N. Moore), pp. 439-455, Purdue University Press, West Lafayette, Indiana.
9. Gordon, A.G. and Rowe, D.C.F. (1982). Seed manual for Ornamental Trees and Shrubs, Forestry Commission Bulletin 59, 132 pp. HMSO, London.
10. Gutenev, V.I. and Bogoroditskii, I.I. (1975). [An effective new method.] Sadovodstvo, 12, 13-14. (From Horticultural Abstracts, 1976, 46, 8935.)
11. Martin, G.C., Mason, M.I.R. and Forde, H.I. (1969). Changes in endogenous growth substances in the embryos of Juglans regia during stratification. Journal of the American Society for Horticultural Science, 94, 13-17.
12. Matton, W.R. and Reed, C.A. (1924). Black walnut for timber and nuts. USDA Farmer's Bulletin No. 1392, 30 pp.
13. Mémmédov, B.A. (1976). [Preparation of walnut seeds for sowing.] Temat. sb. Tr. Azerb. NII Sadovodstva, Vinogradarstva i subtrop. Kul'r, 9, 23-28. (From Horticultural Abstracts, 1977, 47, 11233.)
14. Muenscher, W.C. and Brown, B.I. (1944). Storage and germination of nuts of several species of Juglans. Northern Nut Growers Association Annual Report, 34, 61-62.
15. Sharma, S.D. and Chauhan, J.S. (1981). Effect of shell thickness on seed germination and growth of seedlings obtained from the nuts of seedling walnuts. South Indian Horticulture, 29, 87-89.
16. Sinha, M.M., Pal, R.S. and Koranga, D.S. (1977). Studies in the seed germination of walnut (Juglans regia L.). Progressive Horticulture, 8, 69-74.
17. Williams, R.D. (1980). Period in stratification hastens germination of black walnut seed. Proceedings of the Indiana Academy of Science, 89, 94.
