CONSERVATISM AND VARIABILITY IN SEEDLING OF DICOTYLEDONS 1 23 
By far the most common condition at the cotyledonary node is 
that shown in figures i and 2 and in figure 4, c, and d, where the 
bundles of the epicotyl arise entirely in the intercotyledonary plane 
and the traces of each cotyledon make but a single gap in the vascular 
ring. This corresponds to the unilacunar nodal type in the mature 
Fig. 3. Echinops sphaerocephalus (Compositae). Serial sections from root to 
cotyledon, a, root; b-e, hypocotyl; f-g, node (showing trilacunar insertion of 
cotyledonary traces); h, epicotyl and cotyledons. (Xylem black, phloem white.) 
stem. A number of families, however, show a more complex condi- 
tion, the epicotyledonary bundles arising between the individual 
strands of a cotyledonary trace. In figures 3 and 4, e, the trace has 
four strands and the epicotyledonary bundles arise between each 
lateral and its adjacent central bundle. The vascular supply of each 
cotyledon thus causes three gaps in the ring (in this case two lateral 
traces arise from the same gap) and thus corresponds to the trilacunar 
condition of the mature stem. Several variations on this type were 
observed. In some cases, bundles of the epicotyl appear at the inter- 
