Xll RUDIMENTS OP BOTANY. 



35. Leaf-buds are of two kinds ; the regular only found in the axil* 

 of the leaves ; and the adventitious which may be produced wherever 

 there is an anastomosis of woody fibre. 



36. Leaf-buds have sometimes been confounded with roots by old 

 botanists. A bulb is a leaf-bud. 



37. Leaves are those expansions which issue laterally from the stem 

 and branches of plants. They take their origin from the bark, and are 

 always to be observed, whether perfect or rudimentary, immediately 

 below the leaf-buds. 



38. Those leaves situated near the root are often larger, and of a dif- 

 ferent shape from those higher up the stem ; the former are termed 

 radical, the latter cauUne. 



89. A leaf consists of a petiole, a lamina or limb, and a pair of sti- 

 pules ; but sometimes only one of these three part? can be observed. 



40. The petiole is the channel through which the vessels of the leaf 

 are connected with those of the stem ; it is formed of one or more 

 bundles of spiral vessels and woody fibre, enclosed in a cellular integu- 

 ment. 



41. The lamina of a leaf is an expansion of the parenchyma of the 

 petiole, and is transversed by veins which are ramifications or exten- 

 sions of the bundles of vascular tissue of the petiole, or when there is 

 no petiole, of the stem. 



42. These veins either branch in various directions among the paren- 

 chyma, anastamosing and forming a kind of net-work, or they run 

 parallel to each other, being connected by single transverse unbranched 

 veins ; the former structure being characteristic of Exogenous, and the 

 latter, of Endogenous plants. To this the Conjferai and Cycadete form 

 perhaps the only exceptions ; these haying the stems of the Exogen- 

 ous, but the same arrangement of the veins as in the Endogenoe. 



43. The principal vein of a leaf is a continuation of the petiole, run- 

 ning in a direct line from the base to the apex of the lamina, and is 

 called the midrib. 



44. The lamina is variously divided and formed ; it is usually thin 

 and membranous, with a distinct upper and under surface, but some- 

 times becomes succulent, when the surfaces cannot be distinguished. 



45. A leaf is either simple or compound ; simple when its lamina is 

 undivided, or when, if separated into several divisions, these segments 

 are not articulated with the petiole ; compound when the lamina is ar- 

 ticulated with the petiole. 



46. The modes in which leaves are divided are distinguished by par- 

 ticular names, as pinnate, pinnatifid, bipinnate, bipinnatifid, &c. &c. 

 These terms apply to the mode of division, and are equally applicable 

 to simple and compound leaves. 



47. Stipules are those small foliaceous organs sometimes situated on 

 each side at the base of the petiole. They never occur in the Endo- 

 genae, nor in any Exogenous plants that have sheathing petioles, and 

 are rarely found in genera with opposite leaves. They are sometimes 

 transformed into leaves ; they sometimes have leaf-buds in their axils ; 

 and sometimes also they are changed into spines. 



