Macrosporogenesis and Development of the Macrogametophyte of Solanum tuberosum

Abstract

1. A single archesporial cell, hypodermal in origin, may function as a macrospore mother cell. Frequently, however, a multiple archesporium is differentiated from hypodermal and subhypodermal cells of the nucellus. In such case each archesporial cell may function as a macrospore mother cell, but usually only one of them so functions. 2. A linear row of four macrospores is formed. The chalazal macrospore develops into an embryo sac; the other three spores disintegrate. 3. The micropylar cells of the nucellus break down and the developing embryo sac comes into contact with the inner epidermis of theintegument, which functions as a nutritive layer. 4. In the 4-nucleate embryo sac the spindle persists between each pair of sister nuclei, but no cell plate has been observed at this stage. 5. A typical 8-nucleate embryo sac is formed, at each end of which the four nuclei are connected with one another by fibers from thespindle of the third division as well as by persistent spindle fibers from the second division. 6. Cell division occurs by the formation of cell plates across the spindles of the second and third divisions in the embryo sac. 7. Changes involving degeneration within the ovule may occur at any time during macrosporogenesis and during development of themacrogametophyte. 8. Macrosporogenesis may be accompanied by irregularities in chromosome distribution. Chromosomes, lagging on the spindle, were observed in several instances in both heterotypic and homoeotypic divisions. 9. Degeneration in the microsporogenous tissue may be associated with corresponding changes in the ovules. If degeneration oc-curs late in the anthers, only a small proportion of the developing embryo sacs give any indication of breaking down. 10. Degeneration of mature macrogametophytes occurs frequently. 11. Pollen tubes were not observed in the style of any pistil examined. 12. Degeneration within the ovules may account to a certain degree for the failure of seed formation in the potato.