THE STRUCTURE OF THE SHOOT 



those of the internodes are very vigorous. The leaves 

 on the nodes elongate from the first, but the branches 

 in their axils appear much later. 



As the seedling grows, it prepares for the discharge of 

 the duties which devolve upon it. What we are about 

 to describe of its structure corresponds almost exactly 

 with the structure of each year's 

 twigs of the tree or shrub into 

 which ultimately it develops. 



The two main duties of the 

 stem we have seen to be the 

 support of the head or leaf-bear- 

 ing part of the shoot and the 

 transport of the water and 

 mineral compounds absorbed 

 by the roots to the seat of con- 

 struction of organic substance. 

 Both these objects are carried 

 out by the arrangements in the 

 central cylinder, and both de- 

 pend upon the development of 

 vascular strands connected with 

 those of the root. If we look 

 at a longitudinal section of a 

 whole plant we find that these FlG - 

 strands are continuous through- 

 out it though they are arranged 

 differently in its different regions. In the root we found 

 the strands of wood lying sometimes separately in a 

 central ring, sometimes joined to form a solid cone of 

 wood. Other strands, soft in nature, known as bast, lie 

 between them or between their outer limbs when they 

 are fused in the centre. As we pass upwards we find 

 that in the region just below the cotyledons a certain 

 rearrangement of the strands takes place. The bundles 

 shift their relative positions and the wood strands come 



25. Diagram showing 

 the general structure of a 

 dicotyledonous plant. 



