The Morphology of Araucaria brasiliensis. III. Fertilization, the Embryo, and the Seed

Abstract

1. Pollination occurs on the scale at a distance from the nucellus. 2. The pollen tube is very long and gives rise to many small lateral haustorial branches. It combines features of conifers and cycads to a certain extent. 3. Reasons are adduced to show that this is probably an extremely primitive form of tube, having come down from very remote times little changed. 4. The body cell divides in the extra-nucellar part of the tube a month or more before fertilization. The central cells of the archegonium divides very late or perhaps not at all, except in cases of delayed fertilization. 5. The male cells are very large and unusually active, as well as long-lived. 6. Blepharoplast-like bodies are found in the male cytoplasm. 7. The male cells pass through the neck without injuring the cells. 8. The male cell comes into violent contact with the egg and frequently displaces it. 9. The free nuclear divisions of the proembryo are restricted to the male cytoplasm that surrounds the fusion nucleus, which persists and grows with the proembryo. 10. The male cytoplasm around the older proembryo may be surrounded by a membrane. 11. The number of free nuclei in the embryo varies from 32 to 45 or perhaps more. 12. When walls form the free nuclei are arranged concentrically. 13. The upper peripheral nuclei form the suspensor, the lower ones the cap, and the middle girdle elongates to unite cap and suspensor. 14. The central cells of the proembryo alone take part in forming the embryo. 15. In the growth of the embryonic group the cap is thrust aside and a cylinder of meristematic tissue is organized. 16. The upper portion of the embryonic cylinder functions as a secondary suspensor. 17. The definitive embryo is organized out of a portion of the cells arising from the development of the embryo group of the proembryo. 18. It is dicotyledonous, has resin ducts in the cortex but not in the wood, and is stored full of food materials (large proteid granules and smaller starch grains). 19. The cells of the prothallus become very large and crowded with food. 20. The nucellus persists and becomes a part of the testa of the seed. 21. The embryo continues intraseminal growth after the seeds are shed. 22. It is concluded that, so far as the pollination apparatus and seed structure are concerned, the Araucarineae could be derived from the lycopods, or perhaps from the Cordaitales, but not from the Abietineae. The latter might be derived from a primitive mesozoic stock resembling the araucarians in respect to these features.