THE MORPHOLOGY OF THE VEGETATIVE ORGANS 
STEM 
A. General Characters P 
Under the heading of “Stem” may be classed several parts of 
the plant, all of which are cauline in their morphology and origin, 
but differ to some extent in their functions and relations to the 
other parts of the plant. The horizontal axis, which lies prostrate 
on the soil, bearing the roots and upright shoots, may be termed 
the rootstock;1 the axis of the upright shoot may for convenience 
be designated the stem; the parts which bear the flowers and fruit 
we may speak of respectively as peduncle, rhachis, and stipe. 
In general, all these parts are slender, terete, and of a whitish 
color, although the stem at times assumes a greenish tinge due to 
a small content of chlorophyll. 
I shall consider first the branching and anatomy of the stem and 
rootstock; next, the development of the stem structures which are 
connected with the production of flowers and fruit, comparing 
their anatomy with that of the first two structures. 
B. Branching 
1. Branching in Ruppia maritima. 
Two principal systems of branching occur in Ruppia: one in stem 
and rootstock and connected with the ordinary growth, which we 
may call the vegetative branch system; and the other in the stem 
only, and associated with the production of flowers, which we 
may therefore designate the inflorescent branch system. 
a. Vegetative Branch System. 
The vegetative branch system is a distichous monopodium, the 
branches being borne alternately on opposite sides of the axis and 
in the same plane. In the rootstock, indeed, except near its grow- 
ing point, this initial arrangement is generally later much obscured, 
due to the upward growth of many of the lateral branches (PI. VII, 
1 As will readily be seen—a point which will be brought out more 
clearly later (p. 82)—the rootstock does not differ from the stem from 
a morphological point of view, either externally or internally; for any 
stem, by becoming horizontal and producing roots at-the nodes, assumes 
the character of what I have termed the rootstock. 
