The idea is so obvious, so necessary and so reasonable that naturally it took endless years for anybody to act on it.

There are thought to be 3,000 kinds of plants endangered to some extent in our country, and everybody has always agreed they should be protected in their natural habitat, if feasible, and given sanctuary in well-staffed gardens as well.

Surely it would be simple enough for the country's major botanical gardens to devote some space and budget to the cultivation and preservation of endangered plants of their own neighborhoods.

And some such gardens have already collected and preserved threatened plants. A garden in California, for example, collected wild irises -- I. inominata, douglasiana, etc. -- as human invasion increasingly threatened their natural ranges.

But what is wanted is something more ambitious, and it is now coming into existence, through the Center for Plant Conservation. This is a grouping of 18 botanic gardens and arboretums throughout the country, each of which will collect, grow, preserve and redistribute the threatened flora of its region.

It will cost an estimated $5,000 for each kind of plant to be sheltered, since more is involved than trotting out and digging up a bush. The plants will have to be studied, facts gathered on its flexibility to various conditions, and a central clearinghouse established through which (in time) full information on thousands of these plants can be retrieved easily by anyone wishing to know about them.

George McCully, president of the group, which has home headquarters at the Arnold Arboretum in Boston, gives credit to two young botanists, Don Falk and Frank Thibodeau, for working the necessary levers. It was necessary to interest conservation institutions, foundations (the Andrew W. Mellon Foundation came up with $200,000) and such an influential group as the Garden Club of America in the plan. Everybody approves -- everybody has always approved -- once people like Falk and Thibodeau take the time and effort to get things going.

There are still, I know, a few people who wonder why "some damned weed" should be coddled at a botanic garden, since it may be less ornamental than a rose and may have no known value.

But then nobody had reason to expect a lifesaving drug to be extracted from an obscure periwinkle of Madagascar, either.

Yet that is not the true and major reason for protecting and saving our native flora. The real reason is that the prevailing view in America is that life is better than death, that the long garland of continuing generations is better than extinction. In the long run -- in the short run, for that matter -- all things die. But while we live it is our business to encourage, applaud and stand in awe of life. Because it is living, it should live. Simple.

And now turning from this great matter, I have a suggestion about daffodils for those unfamiliar with the wonderful kinds now grown, and I think especially of those who might wish to devote nothing more than two tiny patches of ground -- 30 by 40 or 50 inches, say -- to these chief ornaments of March and April.

In the past I have suggested considerable numbers of varieties, most of which must be ordered from specialists, and some of which are expensive. But today's suggestion is limited to varieties readily available in local garden shops in September and October.

The first little patch should be devoted to early-blooming daffodils, and prince among these is 'February Gold,' a moderate-sized yellow trumpet flower with slightly recurved outer petals, very fresh and graceful in the mass. The patch would hold three dozen bulbs, planted six or eight inches apart, about six inches deep. They could remain undisturbed for 10 years or more. If a little variety is sought (though three dozen of the kind mentioned will be as handsome as anything), you could include 'Peeping Tom,' which is generally similar but slightly different, and 'Tete a Tete,' which is only six inches high or so, soft yellow with two or three blooms on a stem. If space is even more than usually precious, you could hold the daffodils down to a dozen or so and use the rest for snowdrops and early crocuses, Siberian squills and blue Greek anemones (A. blanda), all of which bloom with the daffodils.

The second small patch might be given to later varieties. The old white poet daffodil 'Actaea' is as cheap as any daffodil and very beautiful with her flat white petals centered by a small yellow cup edged in red. With this you could plant the solid white triandrus hybrid 'Thalia,' with two or three nodding white flowers per stem. Blooming with these two is 'Geranium,' which has smallish white flowers -- one to four per stem -- with yellow cups, despite its name, and 'Cheerfulness,' with clustered double blooms like double camellias, but only an inch across. There is both a white and a very soft yellow form of this variety and both are easily available. All these late varieties named are fragrant, and they look beautiful together.

The effect is much enhanced if the patches are planted in front of some dark evergreen like yew, holly or box. Both the early and late kinds named are cheap and you can find them without sending off. With me the first of these early kinds opened March 4 this year, and the last ones will finish about April 16, so you see there will be flowers for a considerable time, and don't worry about sudden heats to 80 degrees and freezes to the 20s. All these kinds will take what the weather brings, without complaint or loss of beauty.

To prepare for them, dig the two patches now, while spring is still on your mind, to about 14 inches deep. Incorporate leaf mold (sometimes you can scrape it from alley paving, or from bags of leaves you collected last fall) or a couple of bushels of dampened peat moss per planting site. You could plant something else there for summer, clearing it away about Labor Day and planting the bulbs as soon thereafter as you can find them in the stores.

All these kinds will grow in light woodland, and mine grow on a narrow 40-foot-wide city lot overhung by a very large maple and oak. They bloom before the trees leaf out, making it too shady. So do not be discouraged if you lack a sunny spot. If you have sun, so much the better.