STEM. 113 



rooting stem, Fig. 18. It sends out numerous fibres 

 which penetrate, but derive no nourishment from the 

 plant to which it adheres. The Poison Ivy, Rhus 

 radicans, is a good example of this variety. The 

 Voluble stem twines around other plants for support, 

 and if it follows the apparent motion of the Sun, as in 

 the Honeysuckles, Fig. 19, it is said to twine from left 

 to right, and from right to left, when as in Bindweed 

 Convolvulus Septum, it pursues the opposite direction. 

 Some stems are straight as in the Lily ; some diffuse, 

 having irregular spreading branches ; and some are 

 flexucse or zigzag, forming obtuse angles at every joint, 

 as in various species o! Smilax or Green-Briar. When 

 a stem is regularly and repeatedly divided into pairs, 

 Fig. 16, as in common Chickweed, and Stramonium, it 

 is said to be dichotomous or forked. 



With respect to Form, the stem is usually terete or 

 round ; sometimes it is compressed, having its two opposite 

 sides flattened ; and sometimes it is ancipital, or two 

 edged, forming two opposite and acute angles, as in the 

 Blue-eyed Grass. In other cases it is triangular, 

 square, or pentangular, but these terms require no ex- 

 planation. When the angles of a stem are extended 

 into a flat leafy border, as in the Sweet Pea and many 

 of the Thistles, it is said to be winged, but sometimes a 

 decurrent leaf causes the stem to appear winged when 

 in reality it is not. 



The Branches of a stem are alternate, when be- 

 tween two on one side there arises an opposite and 

 intermediate branch ; and they are opposite, when 

 two branches arise at equal distances from the base 

 of a stem. When opposite branches alternately 

 cross each other at right angles, as in the Lilac, they 

 are said to be brachiate or decussate. When several 



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