TRACHEARY ELEMENTS OF THE FERNS. I. FACTORS WHICH INFLUENCE TRACHEID LENGTH; CORRELATION OF LENGTH WITH EVOLUTIONARY DIVERGENCE

White , R. A. (U. Michigan, Ann Arbor.) Tracheary elements of the ferns. I. Factors which influence tracheid length; correlation of length with evolutionary divergence. Amer. Jour. Bot. 50(5): 447–455. 1963.—To determine the variability of tracheid lengths in ferns, several factors were surveyed which might modify them. On the basis of average lengths based on from 100 to 300 measurements, the following factors were found to affect fern tracheid length significantly: location in the plant, stage of maturation of the plant, length of the internode, ploidy, and habitat. These factors were considered when a statistical analysis was made of the relationship between tracheid length and taxonomic divergence among the species of ferns. A Pearson's correlation coefficient was computed, based on average tracheid lengths from 221 species of ferns, and a divergence index based on 8 characters accepted as indicators of specialization or primitiveness in the ferns. A statistically significant correlation (at the 5% level) between length and divergence was found for root tracheids, but not for rhizome or petiolar tracheids. A better understanding of fern evolution is necessary before a more precise picture of length correlation and divergence in the ferns can be obtained.