Waverley Root's great erudition and talent have won him, in the hearts of food lovers, a place by M. F. K. Fisher. His Food of Italy, Food of France, (Knopf) and Eating in America, (Morrow, $16.95) are classics. So should be his two latest volumes. Food (Simon and Schuster, $24.95) is the author's personnal promenade through the alphabet. Like Alexandre Dumas' Dictionnaire de Cuisine, it is witty, idiosyncratic, and highly enjoyable. Herbs and Spice (McGraw-Hill, $19.95), a visually gorgeous book, teaches us everything about the history, geography, growing, processing, and use of every flavorful seed or grass. Because many authors have contributed to it, there are minor inconsistencies. All make superb gifts.