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Abstract
The development of the sporoderm in Asimina triloba before the dissolution of callose proceeds as follow: 1) the initiation and accumulation of prematrix substances, 2) the establishment of the “phantom of ectexine”, 3) the prematrix formation of double origin: microsporal and tapetal, 4) the differentiation of primexine matrix and the beginning of protosporopollenin accumulation on the primordial lamella of the foot layer and in protectum, 5) the differentiation of procolumellae in primexine matrix. The sequence of events corresponds to the general scheme of Dickinson, but the peculiar feature is the formation of prematrix prior to appearance of the ordinary primexine matrix.
