SECTION 16.] ANATOMICAL STRUCTURE. 



135 



have transversely elongated thin places, parallel with each other, giving 

 a ladder-like appearance, whence the name. 



Annular ducts (Fig. 457) are marked with cross lines or rings, which 

 are thickened portions of the cell-wall. 





466 457 



Spiral ducts or vessels (Pig. 453-455) have thin walls, strengthened by 

 a spiral fibre adherent within. This is as delicate and as strong as spider- 

 web : when uncoiled by pulling apart, 

 it tears up and annihilates the cell- 

 wall. The uncoiled threads are seen 

 by gently pulling apart many leaves, 

 such as those of Amaryllis, or the 

 stalk of a Strawberry leaflet. 



Laticiferous ducts, Vessels of the 

 Latex, or Milk-vessels are peculiar 

 branching tubes which hold latex or 

 milky juice in certain plants. It is 

 very difficult to see them, and more 

 so to make out their nature. They 

 are peculiar in branching and inosculating, so as to make a net-work of 

 tubes, running in among the cellular tissue; and they are very small, 

 except when gorged and old (Fig. 460, 461). 



FIG. 453, 454. Spiral ducts which uncoil into a single thread. 455. Spiral 

 duct which tears up as a band. 456. An annular duct, with variations above. 

 457. Loose spiral duct passing into annular. 458. Scalariform ducts of a Fern; 

 part of a bundle, prismatic by pressure. 459. One torn into a band. 



FIG. 460. Milk Vessels of Dandelion, with cells of the common cellular tissue. 

 461 Others from the same older and gorged with milky juice. All highly mag- 

 nified. 



