Abstract
Unlike abundantly-leafed mature plants, 2- to 3-leafed young onion seedlings (Allium cepa L. cv. Senshu-Chuko) showed no swelling of leaf sheaths even when they were kept under long-day conditions. When their roots were excised, however, the seedlings showed sign of swelling. Before swelling became evident, changes in the arrangement of cortical microtubules occurred in leaf sheath cells. The microtubules, which were oriented transversely to the cell axis in unexcised seedlings, were oriented longitudinally or obliquely in excised seedlings. Such effects of root excision were observed only in seedlings grown under long-day conditions, but not under short-day conditions.