The Flora of the Hermit Shale in the Grand Canyon, Arizona
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. 1927 Aug;13(8):574–575. doi: 10.1073/pnas.13.8.574
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PDF![574](https://cdn.ncbi.nlm.nih.gov/pmc/blobs/7c18/1085121/e55c9890cd43/pnas01833-0012.png)