96 
HISTOLOGY OF VEGETABLES. 
seen simple ovoid cells containing a spiral fibre; let 
one of these become elongated and pointed, and we 
have at once the typical spiral vessel. Other arrange- 
ments of the secondary deposit produce the annular, 
the reticulated, the barred or scalariform, and the dotted 
ducts of botanists. That such is the case is demon- 
strated by the occasional presence of the spiral, the 
annular, the barred, and even the dotted variety in 
different parts of the same vessel. Nothing is more 
common in plants, especially among the Monoco- 
tyledons, than to see the spiral fibre in one part broken 
up into rings, as in a spiral vessel from the Opuntia, 
Fig. 84, a. Spiral vessels are usually pointed at both 
FIG. 84. 
ABC D EFGH 
a, short spiral vessels, with thickened fibre, from Opuntia vulgaris, b, 
a spiral vessel becoming an annular one. c, spiral vessel having a hole at 
one extremity, d, dotted vessel with oblique termination and hole in the 
centre, e, reticulated vessel, f, old spiral vessel with perforations, g, h, 
spiral vessels with fibre running from left to right. 
extremities, but occasionally they terminate somewhat 
abruptly, and a hole is often seen near the extremity, 
