Abstract
atmosphere is drier, where there is more wind and where they may even be struck at times by the rays of the sun. In spite of the hairy coatings that make it easier for them to live in relatively arid locations, they have in the main become adapted to drier conditions by the ability of their cells to lose much of their water for short periods without fatal results. This is much the same line of physiological evolution that has been followed by the desert species of Cheilanthes and Notholaena. These plants have retained all of the morphological features and most of the anatomical ones to be found in their congeners of moister climates. By means of an adaptation which is physiological rather than anatomical, these desert ferns are able to live under nearly the same conditions as the cacti, with their elaborate structural features for meeting conditions of drought. In spite of the great diversity exhibited by the ferns of the world, we must regard them as having been conservative from an evolutionary standpoint, when we contrast them with flowering plants. TUCSON, ARIZONA.
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