Comparative Anatomy of the Moraceae and Their Presumed Allies

Abstract

1. There appears to be a correlation between the presence of sclerotic wood parenchyma cells in the xylem and the presence of sclerotic ray cells, sclerotic tyloses, and thick-walled fibers and vessel elements. 2. The advent of ring-porosity, or of some factor or factors causing ring-porosity, seems to give an impetus to anatomical specialization. 3. Non-septate fibers are more primitive than are the septate type of fibers. 4. The solitary pore arrangement of vessels is more primitive than the various aggregate arrangements, such as pore multiples, pore chains, and pore clusters. 5. In comparative anatomical studies, the secondary xylem of herbs and shrubs must be compared with the secondary xylem of trees taken from a region close to the pith. 6. The Hamamelidaceae are derivatives of the Magnoliales. 7. The Casuarinales, Fagales, and Urticales cannot be considered as primitive groups among the dicotyledons. These three groups are considered to be derivatives of the Hamamelidaceae. 8. The Cunoniales (including the Hydrangeaceae, Grossulariaceae, Escalloniaceae, Cunoniaceae, and Brunelliaceae) are derivatives of the Magnoliales. The Rosales have been derived from some group in the Cunoniales. 9. In the Urticales the Ulmaceae are most primitive, the Moraceae less so, and the Urticaceae are least primitive. The Eucommiaceae are also placed in the Urticales. 10. In the Moraceae anatomical specialization seems to have proceeded from the sub-family Moroideae to the Artocarpoideae to the Conocephaloideae to the Cannaboideae. The tribe Fatoueae of the sub-family Moroideae appears to be the most primitive one in the family. 11. There is no evidence for, and much against, the derivation of the herbaceous Urticales from the Aristolochiaceae. 12. The Rhoipteleaceae do not belong with the Urticales. 13. In general, Hutchinson's system is more in accord with the phylogenetic scheme proposed in this paper than are the other systems. His division of the dicotyledons into a herbaceous line and an arboreal line is not borne out by the facts revealed in the present investigation. 14. In general, the evolution of floral structures seems to be correlated with the evolutionary development of anatomical structures. After the re-arrangement of certain questionable groups, therefore, the classification of the taxonomist and the phylogenetic scheme proposed by the anatomist show striking agreement. 15. There is every indication that the study of anatomy will be of great value in the establishment of a natural classification of the angiosperms.