AMERICAN 
JOURNAL OF BOTANY 
Vol. I July, 1914 No. 7 
INVESTIGATIONS ON THE PHYLOGENY OF THE 
ANGIOSPERMS 
I. The Anatomy of the Node as an Aid in the Classifica- 
tion OF Angiosperms 
Edmund W. Sinnott 
It is generally recognized that during the course of evolution among 
vascular plants certain rather definite organs or regions of the body 
have changed much more slowly than others and hence retain many 
ancient characters which have been lost elsewhere. One of the most 
important tasks before the student of comparative plant morphology 
is to determine where these regions are and in what features they are 
conservative, and thus to aid the phylogenist in picking out those 
primitive and constant characters on which he may construct a natural 
system of classification. 
The reproductive organs, root, young plant, first annual ring, leaf 
and node in various families have all been shown to be regions which 
in a greater or less degree are apt to be conservative in their internal 
or external structure. Among these the anatomy of the leaf, par- 
ticularly at the node where leaf and stem unite, often retains in a most 
striking way features which have been lost elsewhere in the plant. The 
ancient centripetal or " cryptogamic " wood has persisted in the foliar 
bundle of Equisetum (3), the cycads (5), and Prepinus (4) after it has 
disappeared in all other regions, save occasionally in the reproductive 
axis. The presumably primitive number and arrangement of leaf 
bundles persists at their point of insertion at the node in the sigillarians, 
ferns (6), cycads, Cordaitales, Ginkgo and the broad-leaved conifers 
although it has changed greatly in the petiole and blade. 
Since the vascular system of the leaf in the lower orders appears 
so generally to be a region which is slow to change, it is reasonable 
to suppose that in the angiosperms as well it will display a similar 
[The Journal for June (1: 255-302) was issued 3 July 1914.] 
303 
