Spinach flowers are borne in clusters in the leaf axils. They are small and lack petals and so are rather inconspicuous. Male flowers produce pollen which flies into the air like dust, when the flowers open and the plant is jarred. A completely female plant produces no pollen.

The pollen of spinach is small and may be carried far by wind. Varieties should be isolated by 1 mile at least, especially in the direction of the pre-wailing wind. Advantage should be taken of any natural barriers, such as stands of tall trees.

The seedstalks are cut when the late-maturing ones begin to turn yellow. The entire crop dries in windrows. Then it is threshed with a pickup combine.

Spinach is one crop with which fairly high cylinder speeds may be used in threshing.

THE COMMON type of radish, sprouting broccoli, mustard, and Chinese cabbage are annuals in the large cabbage family. Each differs from the others as a vegetable, but methods of producing their seeds are much alike.

The acreage devoted to the production of radish seed often exceeds that of any other member of the cabbage family, including cabbage itself.

All are sown early in the spring in northern sections. They can be planted in the fall in southern areas, as for lettuce. Isolation to prevent cross-pollination by pollen-carrying bees between varieties of any one kind should be about one-fourth mile for market, and 1 mile between stock seed plantings. All should be rogued in their vegetative state. For the production of stock seed of radish, the roots are usually dug, rogued for type, and replanted.

The crops are cut and windrowed when a noticeable proportion of the pods have turned yellow. When dry, they can be threshed with a pickup combine. Threshing radish often is facilitated by having a pair of rubber rollers in the machine to help crush the pods, because radish pods do not split lengthwise as do those of the other cabbage members.

SEED PRODUCTION of the biennial vegetables is more complicated because they have to be carried over into the second year.

The cabbage family includes the largest collection of biennial vegetables. Many of them, including both leaf and root vegetables, can be grown for seed either by seed-to-seed (that is, overwintering the plants in the field), or by storing the crop under cover during winter. Market seed is generally produced by the first method, and stock seed by the latter.

The cabbage family is pollinated by insects. Satisfactory isolation between the different members and between varieties is one of the most difficult and complicated in the seed industry. That is because cabbage, cauliflower, collard, kale, kohlrabi, brussels sprouts, and the annual sprouting broccoli all belong to the same botanical species, Brassica oleracea.

Furthermore, cabbage alone falls into distinct varietal groupings based on head shape, season, and foliage color. Cross-pollination between any of these varietal types or any of the other vegetables within the botanical species inevitably gives rise to noticeable offtype plants. To avoid such crossing, seeds-men try to maintain for market seed production minimum isolation distances, which range from one-eighth mile to 1 mile depending on the kinds of vegetables involved. For plantings of stock seed, a distance of several miles is preferable.

When seed is to be grown from cabbage that is to be stored over winter, the crop is grown the first year much as it would be for market, except that the time of planting must be adjusted so that the head matures just ahead of winter.

The crop is rogued as the individual plants are lifted from the ground. The outer leaves are removed from the head. Plants that meet varietal requirements are placed in storage in a single layer on shallow shelves to reduce losses from decay. Storage temperature should be just above 32 . Relative humidity should be high to prevent dehydration of the cabbage. The crop is replanted in the spring.

In seed-to-seed production, seedbeds of the late varieties are planted first, beginning about May 15, and the early varieties last, about July 15. Plants are transplanted in August to the seed fields in which they overwinter. Highly selected stock seed is essential, as the plants never produce fully mature heads and no opportunity comes to rogue the crop critically. The plants also need some protection from freezing and thawing, even in the Puget Sound area. After roguing is completed, therefore, soil is thrown against the plants so that only the upper part is visible. The partly buried plants can withstand temperatures of 5 to 10 .

Seedstalks develop during the second year if interrelated factors (low temperature, chiefly) have been satisfactory. A cross-cut two cuts at right angles to each other may have to be made in heads of cabbage overwintered in storage to allow the head to burst and the seedstalk to develop.

When a good proportion of the pods of all these cabbage-type crops have turned yellow, the seedstalks are cut individually and piled in windrows, where they may cure one to several weeks before threshing. When dry, the crop threshes easily, and cylinder speeds should not be higher than is necessary. As the seeds of all the crops in the cabbage family are similar, seedsmen take care to avoid mechanical mixtures.

Of the cabbage-type crops, cauliflower has the most exacting climatic requirements. These include uniformly cool and relatively humid atmospheric conditions, without danger of subfreezing temperatures.

AMONG THE other biennial crops are a number of fairly important vegetables. They are not related botanically, but they are root or bulb crops and are grown for seed by similar cultural methods. They are carrots, onions, garden beets, turnips, and many related crops of less importance. Seed of all of them is produced either by root (or bulb)-to-seed or seed-to-seed methods.

In the former, which is consistently used for production of stock seed, the crops are grown the first year in much the same way that they are grown in a garden or for market. With all except anions, time of planting has to be de-laved somewhat so that the roots reach marketable size just before winter storage. Medium-sized roots (or stecklings, as are called) and medium-sized bulbs are preferred to large ones. Storage temperatures should be about 40 for all these crops. Relative humidity should be high, except for onion, for which low humidity is preferable.

WHEN seed is grown by the seed-to-seed method, planting has to be done so that the crop goes into the dormant winter season when the edible root or bulb is only partly developed. Onions should not have formed bulbs. If the crops are developed too far, they are more subject to decay during the winter; if they are underdeveloped, they are more likely to be killed by freezing and thawing during the fall or spring.

Experiments in Utah have shown that moderate or even infrequent irrigation is associated with high seed yields of carrots, the fibrous roots of which extend down 5 feet or more.

In 1946 1950, carrot stecklings were set out for seed production in experiments in which three soil moisture conditions (high, medium, and low) and various spacings were studied simultaneously. Soil moisture stress was recorded periodically by means of gypsum blocks to depths of 5 feet.

The onion, which is shallow rooted, usually responds to fairly frequent irrigation with high yields, but even under low soil moisture conditions, a spacing as close as 9 inches between seed-to-seed rows may triple the yield normally expected when rows are 30 inches or more apart.

Seed yields of onions, turnips, and garden beets often are higher when moderate amounts of nitrogen have been included in the fertilizer.

ALL THESE crops, except beets, are pollinated by insects, so that varieties of each vegetable need to be isolated from others at least by one-fourth mile and much farther when the colors of the roots are different white-rooted and yellow-rooted carrots, for example. The pollen of garden beets, like that of spinach, is carried so easily by the wind that varieties should be separated about a mile for market seed and twice that or more for stock seed.

As garden beets cross easily with Swiss chard, sugarbeets, and stock beets, the distance between them should be at least 2 miles.

Through the development of male-sterile onions (plants that produce no viable pollen), many hybrid varieties of this vegetable are being grown. Some production procedures are similar to those followed in growing seed of hybrid sweet corn. Several rows of male-sterile plants, from which the hybrid seed is harvested, are planted for each pollen row. A good supply of honey bees is essential for satisfactory yields. To avoid mechanical mixtures; the seed of the pollen rows should be removed before the hybrid seed on the other rows is harvested.

In all production of onion seed, the seed heads have to be handpicked and cured before threshing. Some growers cure the heads on canvases or in trays exposed to the sun. Others dry the crop indoors in a stream of warm air.

The plants of carrot and beet are pulled and windrowed when a good proportion of the seeds have turned brown. Turnip is pulled when the pods are turning yellow or a few have dried. Curing may require 4 or 5 days or much longer, depending on the weather and the maturity of the crop when it is harvested. A combine with pickup attachment is suitable for all three. In some dry localities, where turnip matures during July, the crop can be combined like grain as it stands in the field without too much loss from shattering.

LESLIE R. HAWTHORN, horticulturist, Vegetables and Ornamentals Branch, Crops Research Division, Agricultural Research Service, is stationed at Logan, Utah, and conducts research in the production of vegetable seed in cooperation with the Utah and Idaho Agricultural Experiment Stations.