THE PLANT BODY 



25 



with the leaf type considered primitive— simple and pinnately veined. 

 Support for the primitiveness of the trilacunar node was found in the 

 dominance of this nodal sti-ucture in the Archichlamydeae, with elabora- 

 tion to multilacunar types (Fig. 6D) in the Epacridaceae, Platanaceae, 

 Araliaceae, Umbelliferae, Polygonaceae, and Meliaceae, and to reduc- 

 tion types in the Centrospermae, Myrtiflorae, and most of the Meta- 

 chlamydeae. Some Archichlamydeae show reduction in trace number 



Fig. 6. Diagrams showing evolutionary development in nodal angiosperm anatomy 

 from a primitive type. A, unilacunar with two traces; B, unilacunar with two traces 

 fused; C, trilacunar, with three traces, the median a double trace; D, multila- 

 cunar with seven traces; E, unilacunar with three traces from one gap; F, five 

 traces from one gap; G, unilacunar with one massive trace of five to seven fused 

 traces. {After Canright.) 



within the family — Leguminosae, Anacardiaceae; and some Metachla- 

 mydeae, multiplication of traces— Epacridaceae. Further evidence sup- 

 porting the primitiveness of the three-trace node was seen in the pres- 

 ence of these nodes in seedlings of dicotyledons that have many traces 

 in the mature plant. The monocotyledons are commonly multilacunar, 

 but seedlings frequently have three-trace leaves, and their carpels, usu- 

 ally multitrace, may have, as reduction forms, three traces or only one. 

 The two-trace, unilacunar node (Fig. 6A)— a "fourth type" of node 

 —was long overlooked. Certain two-trace organs — cotyledons, stamens 

 in a few taxa, carpels with double midribs, set aside as abnormalities 



