Schizogenous secretory cavities of Citrus limon (L.) Burm. f. and a reevaluation of the lysigenous gland concept

The lysigenous appearance of Citrus limon (L.) Burm. f. secretory cavities is the result of fixation artifacts. The glandular epithelial cells of lemon glands undergo rapid destructive swelling when immersed in commonly used fixatives. The swelling is most evident with mature glands, causing a false impression that the epithelial cells undergo autolysis as they complete their development. Epithelial cells of secretory cavities sliced open during tissue preparation show more extensive swelling than those left intact during fixation, indicating a possible cause for inconsistencies among reports of Citrus gland development. Aqueous primary fixation of intact secretory cavities results in sufficient epithelial cell swelling to give a false impression of precocious senescence; osmium vapor-fixed glandular cells show less swelling, contain intact organelles, and appear living at gland maturity. Although the concept of lysigeny is very old, recent evidence for lysigeny is based on investigations that used standard aqueous fixatives. Since fixation requirements for glands from other species of plants could be similar to those for Citrus glands, we suggest that lysigeny, in general, could be a false category of gland development, representing misinterpretation of artifacts.