Anatomy of Cheilanthes tenuifolia

1. The apex of the rhizome is occupied by a tetrahedral apical cell. 2. The stelar anatomy of the stem is dictyostelic. The xylem is broken by wood parenchyma. There is no protoxylem present, the first elements to be lignified being large, scalariform tracheids. 3. The amount of phloem present in the stem is small, consisting of a single row of sieve tubes surrounding the xylem, the amount of external being equal to the amount of internal phloem. 4. The pericycle is well developed, and has reserve food within it. 5. The apex of the leaf is occupied by a wedge-shaped apical cell. 6. The vascular strand of the petiole is single and concentric. 7. The petiole may be derived from types with triarch, mesarch protoxylem, described by Sinnott. The medium protoxylem group moves its position, becomes endarch, and finally completely detached. 8. The leaf has the stomata localized to the lower surface, protected by the inrolled margins of the leaf alone. The cuticle and palisade tissue are well developed, while the lacunar tissue is reduced. 9. The root is endogenous in origin, and is formed by segments cut off from the three-sided apical cell. 10. The root is diarch, new branches arising in two lines corresponding to the ends of the xylem plates. The phloem is poorly developed, while the pericycle is well developed. 11. The sori are marginal, and are protected by the inrolled margins of the leaf; no true indusium is present. 12. The development of the sporangia corresponds mainly with that found in the other Mixtae. 13. The mature sporangium has a vertical annulus interrupted by the stalk.