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A TEXTBOOK OF THEORETICAL BOTANY 



three nodes, and as these are very close together the effect is often that of a 

 whorl of branches all seeming to come from the node of the parent stem. 

 This adds to the density of the bush (Fig. 752). 



The growth of the internodes is independent and is due to a pale-coloured 

 meristematic zone at the base of each. At the end of the growing season 

 the meristem in some species hardens into an abscission layer and the branches 



Fig. 751. — Ephedra nebrodense. Shrubby habit of plant. 

 Kew Gardens. 



drop off, to be replaced next season by axillary shoots.* These species may 

 be called deciduous, by analogy with trees which drop their leaves in winter. 

 The apex of each branch is formed by a bud consisting of the first four or 

 five undeveloped internodes, wrapped in the scale-like leaves. 



Anatomy of the Stem 



The surface of the stem is ribbed. There is a very thick epidermis, 

 which is supported below the ribs by groups of fibre cells. Stomata, each 

 sunk in a circular pit, occur in the furrows between the ribs. They open into 

 a cortex which is differentiated into a loose, outer palisade layer and an 

 inner spongy tissue, both containing chlorophyll and being responsible for 

 all the effective photosynthesis carried on by the plant. An endodermis 



* A sirnilar abscission occurs in the Poplar and the Oak and has been called cladoptosis, 

 as the abscission of leaves is called phylloptosis. 



