12 INTBODTJCTION. 



plants, which is named the Straw or Culm. It presents the 

 following varieties : 



Jointed, with cylindrical hollow parts, united by a contracted 

 solid part. (Fig. 16.) 



Knotted, when the joints are enlarged. (Fig. 17.) 



Geniculate or Kneed, when the joints are bent like a knee. 

 (Fig. 18.) 



It may be solid, round, triangular, smooth, rough, hairy, or 

 downy. 



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

 Radical Peduncle, (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 cellular, fibrous, vascular, and 

 more or less pulpy. They are organs of respiration, absorp- 

 tion, 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 prepared. 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 or petio- 

 late. (Fig. 21.) 



The Leaf-stalk or Petiole is either simple, that is, undi- 

 vided ; or compound, that is, variously branched or divided. 

 It is commonly channelled on the upper side, and frequently 

 enlarged at the base. 



With respect to situation and position. Leaves are 



Radical or Root-leaves, when they arise from the top of the 

 root, or from a very short stem. (Fig. 19.) 



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

 23, 24.) 



