A century ago rhododendrons and azaleas (both are classified as rhododendrons) were rarely grown in American gardens. There were only a few native species and a small group of ironclad hybrids developed in England from which to choose.The ironclads were introduced in 1876 and were so-called because they had the ability to adapt to the climate of the Atlantic Coast.

Rhododendrons are climate-specific and lack the general adaptability of other garden flowers such as roses and marigolds. Successfully adaptable new varieties had to come from those bred and raised in the same region where they were to grow.

Thus it fell to American breeders to produce hybrids that could perform well in their region. For parent stock they used the hardy species and hybrids introduced by plant explorers, brought principally from the East Coast of the Asian continent.

Only seedlings with the right genes survived the three to seven years between their germination and first flowering. Natural selection eliminated the unfit and the hybridizer selected the most beautiful.

The fruits of this process produced a major garden miracle in eastern America during the past 60 years.

The hybridizers who made the major contribution to this miracle were Charles Dexter, patrician New England industrialist; Joe Gable, devout farmer; Guy Nearing, brilliant, nonconforming intellectual; Tony Sharmmarello, inner city kid who made good; and Ben Morrison, scientist-aesthete.

Morrison helped establish the U.S. National Arboretum in Washington, and became its first director in 1951. The Morrison Garden there, named in his honor, contains specimens of those he created. This in addition to 65,000 others, mostly created by these hybridizers.

A new book, intended to provide a permanent record of the hybridizers who produced the azalea miracle in America and commemorating their lives and their plants, "Hybrids and Hybridizers - Rhododendrons and Azaleas for Eastern North America," edited by Philip A. Livingston and Franklin H. West, has just been published by Harrowood Books, 3943 N. Providence Rd., Newton Square, Pa. 19073 (256 pages, well illustrated, including more than 100 in full color, at $25).

The book would make a wonderful Christmas present for a rhododendron and azalea-loving friend, and can be ordered direct from the publisher to be sure of getting it in time.

Their hybrids, with appraisals of both qualities and hardiness, and how they were produced, their thoughts on promising prospects for improvements, and much more are here for the hobbyist to read and relish, according to David G. Leach, often referred to as a "hybridizer's hybridizer," past president of the American Horticultural Society, and author of "Rhododendrons of the World."