THE MORPHOLOGY OF THE VEGETATIVE ORGANS 



Stem 

 A. General Characters 



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 ; '^ 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, 



^ As Avill readily be seen — a point ^vhich 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. 



