CHAPTER IV. 
THE STEM. 
24. Stem.—The stem is that portion of the plant which 
is developed from the plumule. It may grow under- 
ground asin the case of the potato, onion, iris, ferns, 
but usually grows above ground. The chief differences 
between it and the root are :— 
(1) The growing point does not end in a root-cap, but 
in a bud. 
(2) It bears leaves and flowers as well as branches. 
(8) The branches arise exogenously (from the sur- 
face) and not endogenously as in the case of roots. 
(4) The vascular bundles have the phloem and xylem 
contiguous, not side by side as in the roots. 
The stem itself is divided into alternate regions. 
(1) Regions which possess lateral out-growths. 
(2) Regions which do not possess lateral out-growths. 
_ The former are called Nopzs, the latter INTERNODES, 
25. Principal Forms of Stems.—A stem is usually 
cylindrical in section and erect. But some stems are 
triangular, square, five-ribbed, etc., others trail on the 
ground, or twine themselves round supports, or climb 
by means of tendrils, etc. The chief forms of aerial 
stems are ;— 
(a) The runner (fig. 22), a stem which creeps along 
39 ; 
