The Sporangia of Thismia americana

Abstract

1. In the microsporangia the sporogenous cells develop from hypodermal masses, 4 in number, in the usual fashion. 2. At maturity the innermost parietal layer appears crushed by the large tapetal cells. 3. There is marked abortion of sporogenous cells in the microsporangia. 4. The division of the megaspore mother cells gives rise to 4 megaspores, the outer 2 oriented at right angles to the long axis of the ovule. 5. The 3 outer megaspores degenerate very soon, disappearing entirely after a short time. 6. The functional megaspore divides in the usual Way, so that eventually an embryo sac of 8 nuclei is produced. 7. Presence of pollen tubes makes fertilization seem likely. 8. The well developed embryo is imbedded in large endo spermcells which are conspicuous in storage contents. 9. In the seed the nucellus makes a conspicuous layer, developing into a cap of tissue at each end.