CHROMATOGRAPHIC INVESTIGATIONS ON THE ALKALOID CONTENT OF NICOTIANA SPECIES AND INTERSPECIFIC COMBINATIONS

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. IDEAS of the evolutionary relationships of ferns are presently in a state of controversy and flux, and there are many differing views. The early classifications of Diels (1899), Bower (1923, 1926, 1928) and Christensen (1938) have been modified and revised by the more recent work of Ching (1940), Copeland (1947), and Holttum (1949). 1 Received for publication August 15, 1962. Part of a dissertation presented to the Horace H. Rackham School of Graduate Studies, University of Michigan, in partial fulfilhnent of the requirements for the degree of Doctor of Philosophy. The advice and assistance of Dr. Paul S. Dwyer, Mathematics Dept. and Statistical Laboratory of the University of Michigan, with the statistical portions of this study, and of Drs. Charles B. Beck and Warren H. Wagner, Jr., throughout the course of this work is gratefully acknowledged. Opportunities to collect research materials were made possible by an H. H. Rackham School Summer Grant, The H. H. Bartlett Fund and N.S.F. Grant G-10846. 2 The author is presently (1962-63) a National Science Foundation Postdoctoral Fellow in Botany at the University of Manchester, England. These later workers have incorporated numerous morphological characters into their systems in an attempt to determine more accurately the relationships in this group. The fact that there are such differing views, however, indicates a need for additional characters of comparative value which can be used in correlation with those already known. Problems of evolutionary relationships in the angiosperms have been approached frequently through the use of comparative anatomical data (Bailey, 1949). Studies of the xylem have been one of the chief sources of information regarding trends of diversification within the higher groups. The works of Bailey and Tupper (1918), Frost (1930a, b), and Cheadle (1943) are major attempts to determine morphological trends in xylem elements which can be applied to the broader problems of evolution in those groups studied. Their conclusions have had a far-reaching effect on our understanding of the systematics of the flowering plants. This content downloaded from 157.55.39.243 on Thu, 06 Oct 2016 04:53:17 UTC All use subject to http://about.jstor.org/terms