Mesclun--the name means "mixed" in French—is the traditional combination of baby lettuces available year-round in most supermarkets. But during spring, when newly sprouted baby lettuces begin to appear at local farmers' markets, it's possible to appreciate the particular characteristics of individual varieties. Bibb is a delicate, buttery leaf; arugula is a long, spiky, mildly bitter one; crisp romaine is ideal for Caesar salads; watercress has a bright, peppery flavor; and mizuna has a gentle spicy zing. And those are just a few of the more widely grown varieties. The distinctive flavor of a green early in the growing season tends to hold as the lettuce matures, but baby greens are sweeter and have a much more concentrated flavor than mature greens. In texture, baby greens are more delicate, refined, and tender than mature lettuces. Best when eaten raw, baby lettuces are ideal in salads and sandwiches, while mature lettuces can withstand the heat of cooking. Most farmers sell both individual baby greens and mixed greens, allowing you to pick and choose as you please.