Morphological and Histological Studies on Flower Bud Differentiation and Development in Japanese Pear (Pyrus serotina Rehd.)

Abstract

In order to clarify the mechanism of flower bud differentiation in Japanese pear (Pyrus serotina Rehd.), the processes of differentiation and development of the flower bud in the spur of `Nijisseiki' pear were followed morphologically and histologically. 1. There was no increase in the number of nodes in the buds from May 30 to June 20, but thereafter, there was a rapid increase. Twelve scales were formed on June 20 and the first visible signs of flower bud differentiation were observed on June 25. 2. From June 15 to June 20 the diameter of the apical meristem in the buds expanded by one and a half times due to cell division and cell expansion. At the same time, the number of rows of cells forming the tunica was reduced, but in the corpus the number markedly increased. 3. The increase in the number of cells in the corpus led to swelling and thikening of the apical meristem from June 25 to June 30, and simultaneously the primordia of bract and floret (lateral flower) in it's axil began to form in the peripheral meristem. 4. On July 10, the primordium of the inflorescence was completed and that of the sepal initiated. Thereafter, the petal primordium was initiated on July 20 and that of stamen, on July 30. From these results, it was concluded that flower bud differentiation in Japanese pear is determined by the histological changes in the apical meristem (histological differentiation) after the formation of twelve scales, particularly, by the increase in the activity of cell division in the corpus layer and by the increase in the number of nodes