CONSERVATISM AND VARIABILITY IN SEEDLING OF DICOTYLEDONS I25 
vascular tissue of the epicotyl arising somewhere between separate 
strands of the same trace. This condition, it should be noted, is not 
simply that of "independent laterals," which may occur in either of 
the main forms we have described. 
These two types of cotyledonary node are very constant through 
large groups. The unilacunar is much the more common and is 
invariably present (as far as the writer has observed) in 73 out of the 
86 families examined. The multilacunar type was found in the 
Aceraceae, Berberidaceae, Compositae, Euphorbiaceae, Hippocasta- 
naceae, Magnoliaceae, Melianthaceae, Plumbaginaceae, Polygonaceae, 
Proteaceae, Sapindaceae, Sapotaceae and Umbelliferae. In the 
Berberidaceae (Berberis) the two lateral strands of the trace are very 
small and are frequently absent, giving a unilacunar condition. In 
the Magnoliaceae several genera are unilacunar, as is Securineca 
in the Euphorbiaceae. All the other genera and species of these and 
the other families named were invariably found to be multilacunar, of 
one type or another. In the Aceraceae, Sapotaceae and portions of 
other families there are two gaps at the node; in the others, prevail- 
ingly three. 
Since the size of the seedling has been shown by Hill and de Fraine 
(i) to affect the number of protoxylem clusters in the root and hypo- 
cotyl and the number of strands in the cotyledonary trace (the larger 
the seedling, the greater the number) it might also be expected to 
affect the topography of the node. In very tiny seedlings it may 
do so, but in no case observed was this found to be true. Some very 
small seedlings were studied in the multilacunar families, particularly 
in the Compositae and Umbelliferae, but these were always multi- 
lacunar. Many of the largest seedlings, on the other hand (notably 
the Leguminosae as a whole), are unilacunar. 
There is an evident relation between the structure of the node in 
the main stem and that in the seedling. All families in which the 
seedling shows a multilacunar condition possess this type in the 
mature stem also, except in the case of the Sapotaceae. In the 73 
families where the cotyledonary node is unilacunar, however, the 
connection is less definite, for 34, or 47 percent, have a prevailingly 
unilacunar node in the mature plant; 39, or 53 percent, being multi- 
lacunar. 
These facts indicate that in the topography of the cotyledonary 
node we have a character which is much more constant than many of 
