This bright yellow citrus fruit is oval in shape, with a pronounced bulge on the blossom end. The flesh is juicy and acidic. The lemon can range in size from that of a large egg to that of a small grapefruit. Some have thin skins while others have very thick rinds, which are used to make candied lemon peel. Though the lemon is an excellent source of vitamin C (one provides 40 to 70 percent of the minimum daily requirement), it begins to lose its vitamin power soon after it's squeezed. There's a 20 percent loss of vitamin C after only 8 hours at room temperature or 24 hours in the refrigerator.