Développement du fruit de Prunus virginiana (Rosaceae)

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Abstract
The development of the fruit of P. virginiana L. is followed from full bloom to ripening. The maturation process, which lasts 10 wk is characterized by 3 distinct stages. Two periods of rapid growth (at the beginning and the end of ripening) are separated by a stage of retarded growth. Soon after the fertilization, the mesocarp increases in thickness, owing to an enlargement of the cells of the later tissue rather than by an increase in the number of cells. By the end of the 1st period of growth, the endocarp begins to enlarge. In this situation, the increase of thickness is predominantly due to cell division. At the completion of its development, 2 distinct zones were observed in the endocarp. The inner portion is formed of 6-7 layers of lignified cells extending tangentially along the cavity, while the outer portion is composed of 15-20 isodiametric sclereids. The 2nd stage of the development is characterized by an important delay in growth of the pericarp. However, the cessation of the increase coincides with some important changes in the seed, while the endosperm, and almost simultaneously, the embryo rapidly expand. During the maturation of the seed, we noted that the endosperm cells enlarged, their cytoplasm became thicker, and their arrangement in the tissue appeared more regular. Throughout the 3rd phase of the development, a new period of rapid growth is observed. In the mesocarp, the cells enlarged in the radial direction. The development of the fruit of P. virginiana L. and its vascular patterns have been analyzed in comparison with those of other fruits of Prunus.