THE LEAVES. 1O 



A variety of the Stem is the Stalk, Flower-stalk, or Scape, 

 (Fig. 19.) which springs from the root, and supports the flowers, 

 but not the leaves. It may be 



Simple, or undivided, and bearing a single flower. 



Subdivided, and bearing several flowers. 



Scaly, covered with scales. 



Naked, without scales. 



As to surface, &c., it is named like the Stem. 



OF THE LEAVES. 



The Leaves are organs of an expanded form, almost always of 

 a green colour, internally vascular, and more or less pulpy. They 

 are organs of respiration and evaporation, and it is by the action 

 of the air upon the juices of the plant conveyed into them, that 

 the substances necessary for the growth of all the organs are pre- 

 pared. These substances, in a fluid state, afterwards descend 

 through the leaf-stalk, and the outer parts of the stem. Many 

 plants are destitute of leaves, and are therefore termed leafless. 

 When a leaf has no stalk, it is said to be sessile or sitting. 

 (Fig. 20.) When it is elevated on a stalk, it is said to be stalked. 

 (Fig. 21.) 



The Leaf. stalk or Petiole is either simple, that is, undivided ; 

 or compound, that is, variously branched or divided. It is com- 

 monly channelled on the upper side, and frequently enlarged at 

 the base. 



With respect to situation and position, Leaves are 



Radical otRoot-leaves,vfhen they arise from the root. (Fig. 19.) 



Cauline or Stem-leaves, when they grow on the stem. (Fig. 

 23, 24.) 



Alternate (Fig. 22.), when they come off from the stem one 

 by one in different directions. 



Opposite (Fig. 23.), when they grow opposite to each other in 

 pairs. 



Scattered (Fig. 24.), irregularly distributed. 



Clustered (Fig. 25.), crowded together. 



Remote, when widely separated. 



They may grow two together, in threes, four together, &c. 



B'2 



