Seeds of the following genera usually are extracted by depulping the fruits: Cherries, chokecherries, junipers, mulberries, Osage-orange, plums, tupelos, and yews.

Fruits that require mashing or soaking before cleaning (such as those of the cherries, mulberries, Osage-orange, plums, or yews) usually should not be allowed to ferment. An experienced operator, however, can use slight fermentation to make the process easier.

Seeds that require no extraction are produced by the ashes, basswoods, birches, elms, hackberries, oaks, and yellow-poplar. Some of them, however, need to be freed of chaff or trash. In addition, some of the small fleshy fruits, such as those of the common chokecherry and Russian-olive, often are dried without extraction.

CLEANING IS NECESSARY sometimes to eliminate chaff, trash, adhering fruit parts, or empty seeds and to facilitate seed storage and handling.

Often cleaning is combined with extraction, or a combination of methods may be required. Many seeds can be cleaned satisfactorily by running them through screens, either dry or with running water.

Most conifer seeds have wings that must be removed by hand rubbing, beating or trampling in sacks, moistening and raking, or treatment in dewinging machines or macerators. Treatment must be done carefully to avoid injury to the seeds. Unfortunately no mechanical dewingers yet devised are entirely satisfactory, yet hand methods are too expensive for large-scale use. Dewinging damage therefore is one of the major causes of low-quality seed.

Wings, light chaff, or empty seeds usually are removed by fanning. Most conifer seeds require this treatment in addition to dewinging. Large lots usually are run through standard agricultural or specialized seed fanning or cleaning mills. Some skill is needed to remove the debris but not good seeds.

Flotation in water is the most effective means of cleaning the seeds of most pulpy or fleshy fruits, but is not satisfactory with the junipers, because their seeds float. Sound seeds usually sink, but poor seeds, skins, and pulp either float or sink more slowly. The extracted seeds should be dried promptly after wetting.

The yield of cleaned seeds per loo pounds of fruit as usually collected is called the extraction factor. It is necessary to know this factor and average viability of the seeds to determine the amount of fruit needed for specific sowing or market requirements.

The average extraction factor varies by species and within species as shown below. Some are so variable that they overlap into two or more groups:

1 to 5: Douglas-firs, hemlocks, incense-cedar, larches, mulberries, Osage-orange, pines, spruces, thujas.

6 to 10: Cottonwoods, firs, sweet-gum, American sycamore.

11 to 20: Paper birch, chokecherries, cherries, shellbark hickory, Siberian pea-tree, plums, redwood, Russian-olive, white-cedars.

21 to 40: American beech, yellow birch, boxelder, butternut, catalpas, Kentucky coffeetree, cherries, shagbark hickory, shellbark hickory, honey-locust, junipers, black locust, plums, eastern redbud, Russian-olive.

41 to 60: Baldcypress, boxelder, Kentucky coffeetree, elms, mockernut hickory, Norway maple, sugar maple, oaks, pecan, Russian-olive, black walnut, yellow-poplar.

61 to 80: Ashes, basswoods, boxelder, hackberry, bitternut hickory, mocker-nut hickory, pignut hickory, sugar maple, oaks, pecan, yellow-poplar.

81 to 100: Bitternut hickory, pignut hickory, black maple, red maple, sugar maple, oaks, pecan.

STORAGE OF FOREST TREE SEEDS usually is necessary for a few months up to several years.

Frequently seeds are extracted in the fall and held over winter, although those of species like longleaf pine and the white pines often are sown soon after extraction and cleaning, and white oak acorns must be sown immediately after gathering.

Seeds of some species often must be held for several years because good seed crops occur infrequently.

Storage methods should be used that will maintain high viability. This is a simple matter for some species. It is difficult for others. For many, suitable storage practices are not yet known. With proper storage, seeds of many trees can be kept reasonably viable for 5 to 10 years, and those of a few species have been kept for several decades.

Seeds of the following forest trees can be kept satisfactorily by the oldest and simplest method of storage in sacks or sealed containers at air temperatures: Basswoods, Kentucky coffeetree, black locust, and Siberian pea-tree.

Seeds of many trees, however, keep best at low temperatures in sealed containers. Temperatures between 32 and 41 have given good results, but recent research shows that seeds of several conifers keep better at 0 to 23 than at higher temperatures. At 0 , sealing of the containers appears to be unnecessary and perhaps undesirable.

Before storage, seeds of most conifers should be dried to a moisture content below 8 percent of oven dry weight. Seeds best stored cold and dry include those of the ashes, some aspens, birches, cypresses, Douglas-firs, elms, firs, hackberries, hemlocks, honey-locusts, junipers, larches, black locust, maples (other than silver), Osage-orange, pines, some poplars, eastern redbud, sassafras, sequoias, spruces, sweetgum, sycamore, thujas, white-cedars, yellow-poplar, and yews.

Several other forest trees also have seeds that keep best at low temperatures but at a moisture content above 35 percent. Included are: Beeches, buckeyes, American chestnut, hickories, silver maple, oaks, and walnuts. Many of these seeds can be stored for a few months by mixing them with one to three times their volume of moist peat moss, sand, exploded mica products, or chopped sphagnum moss and placing them in a refrigerator or holding them over winter in the ground under a mulch.

Although they can be stored dry and cold, yellow-poplar seeds have been kept for 8 years without loss in viability by placing them in layers alternated with sand in pits dug in the nursery.

Spring-ripening seeds, such as those of the red and silver maples, often are sown soon after collection in the spring to avoid storage losses. For the same reason, the seeds of many of the fall-ripening species are fall sown.

The short-lived seeds of some aspens and poplars can be kept for several months in sealed containers either under a partial vacuum or with a relative humidity of the air of less than 20 percent.

PRETREATMENT IS NEEDED to overcome the seed dormancy common to many tree species. Such seeds fail to sprout even when exposed to favorable conditions of temperature, moisture,. oxygen, and light unless they are first given special treatment.

Of some 400 species of woody plants studied, 33 percent have seeds that are commonly nondormant, 7 percent have seeds with impermeable coats, 43 percent have seeds with internal dormancy, and 17 percent have more than one kind of seed dormancy.

Among the species that require softening of the seedcoat are most of the legumes, including Kentucky coffee-tree, honeylocust, and black locust.

Species that usually require cold, moist treatment or fall sowing to promote prompt germination include most alders, most ashes, bald cypresses, beeches, most birches, most buckeyes, cherries, American chestnut, Douglas-fir (coast form), firs, hackberries, hemlocks, hickories, junipers, most larches, most maples, mulberries, black oaks, some pines (especially the white pines), plums, sassafras, some spruces, sweet-gum, sycamores, tupelos, walnuts, white-cedar, and yellow-poplar.

Seeds that often require either a combination of seedcoat softening and cold moist treatment or sowing soon after collection in the late summer or early fall are those of black ash, bald-cypresses, basswoods, some junipers, Osage-orange, Digger pine, whitebark pine, eastern redbud, and yews.

A tree species may have both dormant and nondormant seeds or those with more than one kind of dormancy. Unless there is time for tests before sowing, however, dormancy must be assumed and the best treatment given for the suspected condition.

TESTS SHOULD BE MADE to determine seed quality, a necessary basis for specifying the rate at which seeds should be sown to produce a certain number of usable seedlings. Such tests usually concern genuineness, purity, number of seeds per pound, moisture content, and viability.

THE RATE OF SOWING in the nursery and for direct seeding in the field is determined from laboratory tests, as modified by local experience.

Nursery and field germination of forest tree seeds usually is 50 to 80 percent of laboratory germination (in the South it may be 95 percent or higher), but further losses normally occur after germination.

The number of usable seedlings produced per zoo viable seeds sown, therefore, usually ranges from 10 to 60 for conifers and varies even more widely for broadleaf species.

Averages run below 10 for the aspens; 10 to 15 for paper birch, yellow birch, eastern cottonwood, American elm, Russian mulberry, northern white-cedar, and yellow-poplar; 16 to 20 for Japanese larch and redwood; 21 to 30 for American basswood, chokecherries, black locust, Osage-orange, eastern redbud, and Russian-olive; 31 to 40 for boxelder, catalpa, cherries, rock elm, hackberry, eastern hemlock, European larch, Siberian larch, most maples, Siberian pea-tree, plums, most spruces; 41 to 60 for baldcypress, Kentucky coffee-tree, Douglas-fir, honeylocusts, bur oak, pecan, some pines, eastern red-cedar, and tamarack; 61 to 80 for some ashes, American beech, most pines; and 81 to 100 for most oaks and walnuts.

IMPROVEMENT of seed handling is an activity of a number of agencies.

The Food and Agriculture Organization of the United Nations is urging all collectors of tree seeds to supply information on the origin of their seed and has developed a reporting form for that purpose.

Several Federal, State, and industrial forestry agencies have begun to collect most of their seeds from high-quality stands and selected trees. Some have established seed production areas or seed orchards. These and related activities will help to provide more and better forest tree seeds for the forestation of those 50 million acres in the best and the quickest way.

PAUL O. RUDOLF is a research forester in the Division of Forest Management Research, Lake States Forest Experiment Station, maintained by the Department of Agriculture in cooperation with the University of Minnesota at St. Paul. He has been staff specialist in artificial forest regeneration on and forest tree improvement there since 1931 and is the author of numerous publications on those phases of forestry. Mr. Rudolf holds degrees in forestry from the University of Minnesota and Cornell.