VIIL] BOTANY. 33 



VIII. THE STEM. 



48. The stem is formed by the elongation of the 

 plumule of the embryo (Par. 36); its uses are to 

 support the leaves, buds, and flowers, and to form a 

 channel of communication by which the water absorbed 

 by the roots is conveyed to them, and the starch 

 formed in the leaves is distributed over the plant. 



49. The stem usually seeks the light, but not always; 

 for many stems grow underground, elongating, and 

 even branching horizontally; such stems (cowslip, 

 potato) are often mistaken for roots, from which they 

 differ in their mode of growth, and in bearing leaves, 

 buds, and flowers. 



50. A fully developed stem may be simple (most 

 palms) or branched. It consists of nodes and 

 internodes : the nodes are the points from which 

 leaves arise ; the internodes are the intervening por- 

 tions of the stem or branch. The nodes are swollen 

 in many plants (pinks, grasses); in grasses the inter- 

 nodes are usually hollow while the nodes are solid. 



51. The chief modifications of the stem besides 

 the common erect one are 



The twining stem (hop, honeysuckle, convol- 

 vulus), of which some turn to the right, some to the 

 left; but very rarely does one kind of plant turn 

 either way indifferently. This twining habit is the 

 effect of an inherent disposition in the tips of all 

 elongating stems to bend successively towards all the 

 points of the compass; a movement which is very 

 obscure in plants with straight stems, but very marked 

 in those that climb. The tip of such a stem, as it 

 elongates, describes a wider and wider sweeping circle, 



