108 
HISTOLOGY OF VEGETABLES. 
fig. 96. from Herne Bay, as described by Mr. 
Bowerbank,* the markings shown on a 
large scale by Fig. 92, e , are double, 
and extend beyond the outer margin of 
the pore. In all these examples, the 
markings, as in the case of those of 
the woody tissue of Cycas revoluta , 
are produced by the elongation of the 
central portion of the pore. 
In many porous ducts, and more 
particularly in those of the Elm, a spiral 
band co-exists with large bordered pores. A portion of a 
duct exhibiting this peculiar structure is represented in 
Fig. 96. 
Portion of a 
duct from the Elm 
showing pores and 
a spiral band. 
* “Transactions of the Microscopical Society,” Vol. i. 
