THE STEM. 35 



mnnication between them and the root, conducting to them the 

 animal and vegetable substances, salts, and earthy matter, 

 which the radicles by their spongioles imbibe for the nourish- 

 ment of the ]ilant. The influence of light and air, through the 

 medium of the stem, is conveyed from the leaves to the root. 

 Stems Lave a provision for a symmetrical arrangement of 

 leaves and branches ; nodes (from nodus^ a knot), or points where 

 leaf-buds are produced, being placed at regular intervals. Iso 

 such provision occurs in roots, which branch out irregularly, 

 according to the nature of the soil. The intervals between the 

 nodes are called internodes. In the internodes, the fibers of 

 the stem are parallel; but at the nodes, the inner fibers are 

 sent off laterally to form leaf-stalks. The nodes have an in- 

 timate connection with the formation of all leaves smdhiids/ 

 they are the points from which these organs are developed. 

 The stem in the embryo plant has its nodes, to the first of 

 which the cotyledons are attached ; at the next node above, we 

 find the primordial leaves. The distance between the nodes 

 determines the distance between the leaves ; they may be so 

 short as scarcely to be perceptible, or they may be wholly ob- 

 literated, or suppressed, and the leaves brought close together, 

 in bunches, or arranged in whorls round the stem, or two may 

 be situated on opposite sides of the stem. It is a general law 

 in the arrangement of leaves and branches, that they are dis- 

 posed sjm'ally^ in a line winding round the ste7n or axis^ like 

 the threads of a screw, though this arrangement is often inter- 

 rupted by various causes. 



41. All flowering plants have stems in some form 

 or other. Those which have conspicuous stems are 

 said to be caulescent (from caulis^ a stem), as in trees, 

 shrubs, and most annual plants. The caulis is either 

 simple, as in the white lily ; or branching, as in the 

 gerani^um. We have, at Fig. 24, the representation of 

 a caulis^ or proper stem {<^\ a ped^mcle^ or flower- 

 stalk (^), and a petiole., or leaf-stalk {c). Oulm^ or 

 straw (Fig. 25), is the stem of grasses and rushes. 

 The culm is either without knots., as in the bulrush, 

 jointed or knotted., as in Indian corn, gen- 

 icidated^ or bent like an elbow, as in 

 some of the grasses. The bamboo, sugar- 

 cane, and various species of reeds, have 

 stems of the culm kind ; some of them, particularly the bam- 

 boo, are known to attain the hight of forty feet. Scape (Fig. 

 26, (2 a) is a stalk springing from the root, which bears the 



Nodes and internodeg— General rule in the arrangenaent of leaves.— 41. Division of stems— Caulu— 

 Culm— Scapa. 



