On the cover: Cryosection of part of a pea nodule containing lipopolysaccharide-defective Rhizobium leguminosarum bv. viciae mutant strain B633 stained with berberine and aniline blue. Left, bright-field image showing the position of a large invasion structure. The nuclei of cells surrounding this structure are stained with aniline blue dye. Right, the same section observed under UV light. For the article by Perotto et al., see page 99. Photographs by Silvia Perotto.
