452 
EDMUND W. SINNOTT AND IRVING W. BAILEY 
type of leaf -base is the most ancient is therefore intimately connected 
with the parallel question as to which type of nodal anatomy is the 
most ancient. In a previous paper one of the writers has brought 
forward evidence that the trilacunar node is the most primitive 
angiosperm condition. If this theory is the correct one a leaf with two 
independent stipules is evidently more ancient in type than one with 
a sheathing base, the latter having arisen by an increase in basal 
extent of the stipules and their gradual fusion with the petiole. 
As to whether the earliest angiosperms were provided with stipules 
or not we may not be sure. If the leaf margins of these plants were 
devoid of glands or pores, it is very likely that rounded swellings, 
rather than typical stipules, occurred opposite the lateral leaf-traces, 
as in the trilacunar entire families today. On the other hand, if 
primitive angiosperms possessed toothed leaves, it seems altogether 
probable that they were provided with stipules from the first. The 
fact that in so many families of plants stipules bear evidences of reduc- 
tion would rather indicate that they once were a much more conspicu- 
ous feature of angiosperm leaves than they generally are at present. 
Summary 
1. There is an intimate connection between the type of nodal 
anatomy (one, three or many traces and gaps) and the occurrence of 
stipules and similar structures in dicotyledons. In the majority of 
plants with a trilacunar node stipules are present; in almost all with 
a unilacunar node they are absent, and in all with a multilacunar 
node the leaf has a sheathing base. 
2. There is a similar connection in monocotyledons, particularly 
in such primitive forms as the Potamogetonaceae. 
3. The growth of the lateral leaf-trace apparently exerts a stimulus 
which results in the development of the stipule, for the stipule in- 
variably occurs directly opposite the point of departure of the trace. 
4. The character of the leaf margin is also important in governing 
the occurrence of stipules, for stipules are generally absent in entire- 
leaves families, even though the latter are trilacunar. The fact that 
stipules and leaf teeth almost always possess apical pores or glands 
which are usually atrophied after the leaf has reached maturity 
suggests that both structures have essentially the same function. 
5. Morphologically, stipules are to be regarded as integral portions 
of the leaf, and seem to be more nearly homologous with teeth than 
