Development of the unfertilized embryo sac and pollen tubes in the dwarf mistletoe <i>Arceuthobium americanum</i> (Viscaceae)
Bibliographic record
Abstract
Megasporogenesis, embryo sac development, and pollen tubes in Arceuthobium americanum Nutt. ex Engelm. were investigated with light, fluorescence, and electron microscopy. The orthotropous ovular structure of A. americanum lacked integuments and possessed a nucellus that was largely continuous with and indistinguishable from the placenta; we coined this structure the placental–nucellar complex (PNC). Two megasporocytes became evident in the tenuinucellate PNC by mid-April, and had undergone bisporic megasporogenesis by mid-May. The upper cell from each dyad (distal to the base of the PNC) became a functional megaspore, although only one would develop into a seven-celled embryo sac. Like typical angiosperm embryo sacs, that of A. americanum possessed an egg cell having the ultrastructure reflective of a quiescent cell, and lacked cellulosic and (or) hemicellulosic wall material between the egg apparatus and central cell. However, the egg apparatus arose at the lower embryo sac pole, not at the upper as expected for an orthotropous ovule. A hypothetical model for the development of Arceuthobium ovules is the ancestral fusion and subsequent reduction of two anatropous ovules to form two embryo sacs within the PNC, of which only one completes development. The synergids have no role in pollen tube guidance, as tubes could be seen below each functional megaspore prior to megagametogenesis.Key words: Arceuthobium, embryo sac, megasporogenesis, mistletoe, pollen tubes, ultrastructure.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".