SECTION 16. J 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 

 ai'e thickeued portions of the cell-wall. 



Spiral ^w^cX^ 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 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 3f ilk-vessels _ are peculiar 

 branching tubes which hold late.v 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 

 tubes, running in among the cellular tissue ; 

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



4G1 



IS to make a net-work of 

 and they are very small. 



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

 duet which tears up as a band. 456. .\ii annular duct, with variations above. 

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

 part of a bundle, prismatic 1)y pressure. 459. One torn into a band. 



Via. 460. Milk Vessels of Dandelion, with cells of tlie common cellular tissue. 

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

 nified. 



