VASCULAR TISSUE. 



49 



of these duels, shown in place among the woody tissue, are seen 

 to have oblique partitions of the same kind. An examination in 

 the forming state confirms this view ; and in the young stems of 

 herbaceous plants, they may often be separated artificially into 

 their primitive elements. These jointed ducts are occasionally 

 branched, giving further proof that they are aggregations of con- 

 fluent cells. Dotted ducts are usually met with in the wood alone, 

 where they commonly abound. Being of greater calibre than any 

 other cells or vessels found there, they form the pores so conspic- 

 uous to the naked eye on the cross-section of many kinds of wood, 

 such as of Oak, Chestnut, and Mahogany, as well as the lines or 

 channels seen on the longitudinal section. Their size, compared 

 with that of the wood-cells in the wood of the Plane-tree, is shown, 

 both in longitudinal and transverse section, in Fig. 20, 21. 



59. Reticulated, Banded, and Scalariform Ducts are the modifications 



of what is more strictly called vascular tissue ( Trachenchyma of 

 Morren and Lindley) which most resemble dotted ducts ; and 

 which usually take their place, or occur with them, in the stems 

 of herbaceous and small woody plants. There is no important 

 difference between them : indeed, they are often distinguishable 



FIG. 41. Scalariform ducts of a Fern, rendered prismatic by mutual pressure. 



FIG. 42. Similar duct of a Fern, torn into a spiral band. 



FIG. 43. Duct from the Wild Balsam or Jewel- weed; the coils of the thread distant ; a por- 

 tion forming separate rings. 



FIG. 44. A portion of a duct from the leafstalk of Celery ; the lower part annular ; the 

 middle reticulated, and the thread at the upper part broken up into short pieces. 



FIG. 45. A simple spiral vessel, torn across, with the thread uncoiling. 46. Two such ves- 

 sels joined at their pointed extremities. 



FIG. 47. A compound spiral vessel, partially uncoiled, from the Banana. 



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