442 EDMUND W. SINNOTT AND IRVING W. BAILEY 
1. In vascular plants below the Gnetales and angiospeims the 
foliar trace, whether it is a single bundle or is composed of two or of 
many strands, causes at its departure only a single break or gap 
(if any) in the continuity of the woody ring of the stem. 
2. Among angiosperms the nodal topography is much more various 
for there may be a single gap (unilacunar type), three distinct and 
usually distant gaps (trilacunar type), or many gaps (multilacunar 
type). The nodal plan is exceedingly constant within large groups, 
most families and many orders being almost invariably characterized 
by some one of the three types. 
3. From its predominance in the lower Archichlamydeae and 
especially in the presumably primitive Amentiferae, Ranales and 
Rosales, and from its occurrence in the more primitive members of 
otherwise unilacunar or multilacunar families or orders, the trilacunar 
type is regarded as the most ancient angiosperm condition. 
4. The unilacunar node has evidently been derived by a reduction 
of the trilacunar, either through the approximation of the three gaps 
and their coalescence into one; or through the disappearance of the 
two lateral bundles and gaps. 
5. The multilacunar type has been derived by an amplification 
of the three original bundles and gaps into five, seven, nine or more. 
6. The multilacunar node of the monocotyledons has apparently 
been derived from such a trilacunar condition as persists in the 
Potamogetonaceae and in the seedlings of other families. 
The importance of these facts of nodal anatomy in connection 
with the morphology of stipules, sheathing leaf -bases and related 
structures is evident when we observe that in the majority of plants 
with a trilacunar node, stipules are present; that in almost all with a 
unilacunar node, stipules are absent, and that in all with a multilacunar 
node, the leaf has a more or less sheathing base. There is obviously an 
intimate connection between the type of nodal topography and the 
occurrence of stipules. 
The following table^ indicates briefly the facts as to the occurrence 
of stipules and related structures in the more important families of 
dicotyledons, together with the prevailing type of nodal topography 
(and and also of leaf margin) in each. 
* Parentheses indicate an uncommon condition. The three types of nodal 
topography are represented by the figures i , 3 and <» . The prevailing character of 
the leaf margin in each family is noted in cases where both types are not well repre- 
sented. 
