{'fraction_non_alphanumeric': 0.01828410689170183, 'fraction_numerical': 0.0, 'mean_word_length': 5.241228070175438, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
COMPARATIVE STUDIES OF THE NODAL AND VASCULAR ANATOMY IN THE NEOTROPICAL CYATHEACEAE. II. SQUAMATE GENERA

A B S T RA CT Vascular tissue development in the mature stems of the six squamate genera (those with scales as stem and petiole indument) of the Cyatheaceae is described. All squamate genera possess an erect stem, although Cnemidaria approaches an acaulescent condition. The majority of the species studied possesses a spiral phyllotaxy, although a whorled condition predominates in certain species. Adventitious roots arise from the leaf bases and, at irregular intervals, from the stem. Adventitious buds occur in the genera Alsophila and Nephelea and show the same ontogenetic changes as occur in the young sporophytes of tree ferns. Mature stems have a dictyostele with overlapping leaf gaps; this consists of individual meristeles, each surrounded by sclerenchymatous tissue. All genera possess medullary bundles, whereas cortical bundles are found only in certain genera and species. The origin, course, and function of these accessory vascular bundles are discussed. The squamate genera in the Cyatheaceae show striking similarities in both anatomical and morphological characters, and constitute a natural grouping. TREE FERNS were once a dominant part of the world's flora, and today still form a conspicuous part of the vegetation of the tropical rain forests of the world. During the Carboniferous Period