SECTION IG.] ANATOMICAL STRUCTURE. 



135 



have transversely elongated tliiu 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. 



Spiral ducts or vessels (Fig. 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 uncoded threads are seen 

 by gently pulling apart many leaves, 

 such as those of Amaryllis, or the 

 stalk of a Strawberry leaflet. 



Laliciferotis ducts. Vessels of the 

 Latex, or Milk-vessels are peculiar 

 branching tubes which hold latex or 

 uiilky 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 

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

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



so as to make a net-work of 



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, witli cells of the common cellular tissue. 

 46L Others from the same older and gorged with milky juice. All highly mag- 

 nified. 



