450 
EDMUND W. SINNOTT AND IRVING W. BAILEY 
between the character of the leaf margin and the occurrence of stipules 
in those families which have both toothed and entire, and stipulate 
and exstipulate, leaves. In the Saxifragaceae, for example, the entire- 
leaved genera Philadelphus, Deutzia and Hydrangea are without 
stipules, whereas stipules or stipule-like appendages occur in Ribes, 
which almost always has toothed leaves; and also in certain of the 
herbaceous serrate genera. In the Caprifoliaceae the entire-leaved 
genera Lonicera and Diervilla are exstipulate, as are the entire-leaved 
species of Viburnum, but the serrate, dentate or lobed species of the 
last-named genus are in the great majority of cases provided with 
stipules. The Rosaceae are overwhelmingly stipulate, but in the 
sub-family Chrysobalanoideae, which is mainly tropical and entire- 
leaved, stipules are either absent or extremely small. The same fact 
is also evident within single genera, for those species of Salix, 
for example, which are quite entire, have no stipules or have 
very small ones; and Myrica asplenifolia, with its strongly dentate 
leaves, is stipulate whereas the other species, many of which are nearly 
or quite entire, are not provided with stipules. In all these instances 
the node is trilacunar. In many other families, such as the Euphor- 
biaceae, Violaceae, Moraceae and others, the absence or small size of 
stipules in entire-leaved species and their strong development in species 
with toothed leaves is evident. 
The resemblance between stipules and leaf-teeth is still further 
emphasized by the fact that in the young leaf both structures are 
almost always tipped with water pores or with glands, and that these 
pores or glands usually become functionless in the mature leaf. 
Stipules in many cases wither and fall when the leaf comes to maturity. 
The facts seem to point to a similar functional importance, in the young 
and growing leaf, of the terminal organs of both stipules and teeth, 
a function which usually ceases after the leaf has become mature. 
The occurrence of stipules therefore seems to be dependent on 
the structure of both the node and the margin. When the node is 
trilacunar and the margin toothed, stipules are almost invariably 
present; and when the node is unilacunar and the margin entire, 
they are almost invariably absent. The former determining factor 
is evidently the more important of the two, for the presence of lateral 
traces seems to be almost essential to the production of stipules, often 
causing them to be developed in plants the leaves of which are devoid 
of marginal pores or glands. The presence of such a pore or gland, 
