RUDIMENTS OF BOTANY. IX 



23. The bark surrounds the wood, and when fully formed consists in its 

 inner portion of a layer of woody and vascular tissue in the form of rough 

 Woody fibre, constituting the Liber. The outer portion which covers the 

 liber is then also distinguishable into the green layer, and the corky envelope. 

 The whole is covered by the epidermis. 



24. The cambinm is a viscid secretion which is formed in the spring, be- 

 tween the liber and alburnum. 



25. The stem of Endogenous plants presents no distinction of pith, me- 

 dullary rays, wood and bark, but is formed of bundles of ducts and spiral 

 vessels interspersed through a cellular tissue ; and this is surrounded by a 

 stratum of cellular tissue and woody fibre different from bark, inasmuch as 

 it cannot be separated from the stem itself Such plants have their diam- 

 eter increased by the addition of central vascular tigsue and ducts. 



26. Projections from the medullary sheaths sometimes reach the circum- 

 ference of the stem and branches, forming what are called nodes, to which 

 are attached leaves and leaf-buds, and the spaces between these are called 

 internodes. 



27. Whatever is produced by the evolution of a leaf-bud is a branch : a 

 spine therefore is a kind of branch ; it differs from the prickle which is an 

 indurated process of the epidermis. 



28. The stem peculiar to the grasses and other allied tribes is termed a 

 culm. This is simple or rarely branched, generally hollow within or fistu- 

 lous, and separated at intervals by knots or partitions from which issue the 

 leaves. 



29. The stem may be simple or branched, and with the branches may be 

 cylindrical, or conical; round, (terete,) or angled; smooth, furrowed, or 

 rough, or hairy, &c. 



30. With regard to duration the stem is 



a. Annual, ((T)) when it is completely developed and decays during the 

 same season. 



b. Biennial, ((^) when it produces fruit the second season and then 

 decays. 



c. Perennial, (Tj.) when it produces flowers and fruit during many suc- 

 cessive seasons. • 



31. The term Aeri or Aeri«ceo%s employed in opposition \,o perennial, de- 

 notes that the stem generally dies down to the ground every year, 



LEAF-BUDS. 



32. Buds are of two kinds, leaf-buds and flower-buds. 



33. Leaf-buds consist of rudimentary leaves surrounding a vital point, 

 the tissue of which is capable of elongation ; upwards in the form of stem, 

 and downwards in the form of wood or root. 



34. Flower-buds consist of rudimentary leaves surrounding a point, which 

 does not elongate after it is once developed, and assumes when fuliy devel- 

 oped, the form of reproductive apparatus. 



35. Leaf-buds are of two kinds ; the regular only found in the axils 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 the old 

 botanists, A bulb is a leaf-bud. 



Al* 



