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 

 arc thickened portions of the cell-wall. 



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

 a spiral libre 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. 



Laticiferou* ducts, Vessels of the 

 Luffs, or MUk-vesseh are peculiar 

 branching tubes which hold latex or 

 milky juice in certain plant s. It is 

 very difficult to sec them, and more 

 so to make out their nature. They 

 arc peculiar in branching and inosculating 

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

 except when gorged and old (Fig. 1G0, 4G1). 



so as to make a net -work of 



Km. 453, 154. Spiral ducts which uncoil into a Bingle thread. 456. spiral 

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



457. Loose spiral dud passing into annular. 4aS. Sealariforni duets of a Kern; 

 part of a bundle, prismatic by pressure. 4.'V.'. One torn into a band. 

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



401. Others from tlu; same older ami gorged with milky juice. All highly mag- 

 nified. 



