THOMPSON AND BAILEY: TETRACENTR'ON, ETC. 3 1 



have been "reduced" from advanced and more complex types of 

 Angiosperms. 



Summary and conclusions 



Vessels are entirely absent in the secondary xylem of Tetracentron, 

 Trochodendron, Drimys colorata, D. axillaris, and D. Winteri. 



Vestiges of vessels do not occur in the root, seedling, young 

 stem, node, petiole, traumatic tissue, and other regions that have 

 been considered to be retentive of ancestral characters. 



The form, structure, and arrangement of the tracheids of the 

 xylem closely resembles that of the Gymnosperms and there 

 seems to be no valid reason for not considering the three genera 

 primitive as far as their xylem structure is concerned. 



The wood-parenchyma is diffuse in Tetracentron, Trochodendron, 

 and Drimys Winteri. In D. colorata and D. axillaris it shows 

 transitions from diffuse to banded and terminal. 



The distribution of parenchyma in these three genera makes 

 it seem improbable that the terminal parenchyma of the Mag- 

 noliaceae originated through reduction from the vasicentric con- 

 dition. 



There appears to be no reliable evidence to indicate that the 

 Magnoliaceae and allied families are forms that have become highly 

 specialized through reduction from advanced types of Angiosperms. 



In conclusion the writers wish to express to Mr. E. H. Wilson 

 their sincere thanks for material of Trochodendron aralioides, and 

 to Professors A. J. Eames and E. W. Sinnott for material of 

 Drimys colorata and D. axillaris. 



Explanation of plates 2-4 



Fig. I. Ginkgo biloba, transverse section of two year old stem, X 13. 

 Fig. 2. Tetracentron sinense, transverse section of four year old root, X 18. 

 Fig. 3. Trochodendron aralioides, transverse section of seven year old stem, X n. 

 Fig. 4. Tetracentron sinense, transverse section through nodal region of a young 

 stem, X 23. 



Fig. 5. Schizandra chinensis, transverse section of young stem, X 16. 

 Pimis palustris, transverse section of mature wood, X 50. 

 Trochodendron aralioides, transverse section of mature wood, X 40. 

 Trochodendron aralioides, transverse section of seedling stem, X 60, 

 Drimys colorata, transverse section of stem, X no. 

 Sivietenia Mahagoni, transverse section of mature wood, X 30. 

 Tetracentron sinense, transverse section of petiole, X 20. 

 Trochodendron aralioides, transverse section at base of leaf, X 25. 



