Observações citológicas em Coffea. VII - A macrosporogênese na variedade "monosperma"

Abstract

This article deals with the observations made in the ovule and development of the macrogametophyte in Coffea arabica L. var. monosperma. The young ovule is normally constituted by a rudimentary nucellus surrounded by a single and well developed integument. No irregularities are found until the beginning of the first meiotic division in the ma-crosporocyte which is situated inside the nucellus. The two meiotic divisions are very abnormal and during this process, 44,4 % of the otherwise normal macrospores degenerate. Only. a few normal macrospores are formed. The functional macrospore is not always the chalazal one as in the normal coffee varieties. Irregularities occur also in the subseguent divisions in the formation of the embryo sac. Degeneration then increased from 44,4 to 82,0%. Only one complete embryo sac has been found among the 87 examined ovules. During the formation of the embryo sac, even when complete degeneration occurs, the ovule increases in volume due to the multiplication of the integument cells. From the moment in which the embryo sac should be formed (two days after the flower opening) this increase in volume stops. A total desorganization of the ovule occurs around 105 days after the opening of the flower.