Question: what name is used to designate the tubular protrusion from the pollen grain
[{'answer': 'pollen tube', 'provenance': [{'wikipedia_id': '46980', 'title': 'Pollen', 'start_paragraph_id': 1, 'start_character': 479, 'end_paragraph_id': 1, 'end_character': 490, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '46980', 'title': 'Pollen', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 348, 'bleu_score': 0.918221068290973, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7548310193960912262}, 'section': 'Section::::Structure and formation.\n'}]}]