ARE TETRACENTRON, TROCHODENDRON, AND 

 DRIMYS SPECIALIZED OR PRIMITIVE TYPES? 



W. P. Thompson and I. W. Bailey 



University of Saskatcheioan Bussey Institution, Harvard University 



(with plates 2-4) 



The presence of vessels in the xylem of Angiosperms and their 

 absence in that of the Gymnosperms is one of the striking 

 differences between these two great groups of plants. The taxono- 

 mic significance of the absence of vessels in Gymnosperms is likely 

 to be emphasized by the work of Lignier and Tison upon Wel- 

 witschia, and that of Thompson upon Gnetum, which indicates 

 that the Gnetales belong in the former rather than in the later 

 group. This raises the question, are there, among living Angio- 

 sperms, forms that have retained the primitive, Gymnosperm 

 vesselless type of structure? 



Among the Ranales there are four well-established genera, , 

 Tetracentron, Trochodendron, Drimys, and Zygogynum, that, owing 

 to the simplicity of their xylem, have been compared with the 

 Conifers. In 1842 Goeppert noted the absence of vessels in the 

 xylem of Drimys, and his observation has since been confirmed 

 by a number of botanists, notably by Solereder and Van Tieghem. 

 Absence of vessels has also been recorded in Tetracentron, Trocho- 

 dendron, and Zygogynum by Eichler, Harms, V^an Tieghem, 

 Solereder, and others. Opposed to the observations of these 

 investigators are the statements of Parmentier, that vessels occur 

 in Trochodendron and two species of Drimys. However, it has 

 subsequently been shown by Van Tieghem that Parmentier's so- 

 called Drimys Muelleri and D. vascularis were wrongly identified, 

 and undoubtedly do not belong in the genus Drimys. 



More recently, Holden^ has advanced the idea that the Magnoli- 

 aceae are forms that have become specialized through reduction, 

 and, therefore, are not primitive as has been considered probable by 

 a number of botanists and geologists. 



^Holden, R. Reduction and reversion in North American Salicales. Ann. Bot. 26: 

 171. 1912. 



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