XU INTRODUCTION. 



35. A complete leaf comprises the Blade, the Stalk, and a pair of Stipules ; 

 but these three parts are not always present in one leaf. 



36. The Blade, Limb, or Lamina, is the expanded part, and presents a great 

 variety of forms. It is simple, when it consists of a single piece, however cut or 

 divided ; and compound, when of two or more distinct pieces (lea/lets), which 

 separate by a joint. 



37. The Stalk, or Petiole, connects the blade with the stem. When it is 

 wanting, the leaf is said to be sessile. The stalk of a leaflet is called a Petiolule. 



38. The Stipules are appendages of various forms, placed one on each side at 

 the base of the petiole. They are separate, or else united with the petiole, or 

 with each other, when they occasionally form a sheath (Ochrea) around the 

 stem above. The stipules of a leaflet are called Stipels. 



39. The manner in which the veins are distributed through the leaf is called 

 Venation. 



40. There are two modes of venation ; viz. parallel-veined, or nerved, when 

 several simple veins, or ribs, run parallel from the base of the blade to its apex ; 

 and reticulated, or netted-veined, when the veins divide into numerous primary and 

 secondary branches (veinlets), which again unite to form a kind of network. 



41. The latter mode embraces both the pinnately veined, or feather-veined leaf, 

 where the petiole is continued through the middle of the blade, giving off at in- 

 tervals lateral veins ; and the palmately veined or ribbed leaf, when it divides at 

 the apex into three or more strong branches. 



42. The manner in which leaves are divided corresponds with that of their 

 venation. 



43. A simple pinnately veined leaf becomes pinnatifid, when the incisions 

 (sinuses) extend about half-way to the midrib, or continuation of the petiole ; 

 and pinnately divided, when they extend down to the midrib. A compound pin- 

 nately veined leaf is, of course, pinnate, with the separate leaflets arranged on 

 each side of the common petiole. When this is terminated by a leaflet, the leaf 

 is said to be odd-pinnate, or unequally pinnate, and when it is wanting, abruptly 

 pinnate. 



44. So, also, the palmately veined leaf becomes palmately cleft or divided, 

 when the incisions are directed toward the base of the blade. When the divis- 

 ions consist of separate leaflets, it becomes palmately compound. 



45. Floral leaves, or those from the axils of which the flowers are developed, 

 are called Bracts ; and those which are borne on the flower-stalk, Bractlets. 



6. The Flower. 



46. A Flower consists of those parts, or organs, which are concerned in the 

 production of seed. Like the leaf, of which its parts are a modification, it is 

 developed from an axillary or terminal bud. 



47. The manner in which the flowers are arranged on the stem or branches is 

 termed the Inflorescence. 



48. There are two modes of inflorescence ; viz. the indefinite, or centripetal, 

 where the flowers all arise from axillary buds, the lowest or outermost expand- 

 ing first, while the axis elongates indefinitely from the terminal bud ; and the 

 definite, or centrifugal, where the flowers arise from the terminal bud, first, of the 

 main axis, and successively from that of the branches. 



