32 
ORGANOGRAPHY. 
BOOK I. 
it; such as the veins of leaves, and petals, and of all other 
modifications of leaves. It has been supposed that they are 
never found either in the bark, the wood, or the root ; and 
this appears to be generally true. But there are exceptions 
to this: Mirbel and Amici have noticed their existence in 
roots; and Mr. Valentine and Mr. Griffith have both ex- 
tracted them from the root of the Hyacinth ; they do not, 
however, appear to have been hitherto seen in the roots of 
Exogens. I know of no instance of their existence in bark, 
except in Nepenthes, where they are found in prodigious 
quantities, not only between the alburnum and the liber, em- 
bedded in cellular tissue, as was first pointed out to me by 
Mr. Valentine, but also sparingly both in the bark and wood. 
They have been described by myself as forming part of the 
testa of the seed of Collomia, and Brown has described 
them as existing abundantly in that of Casuarina. In the 
former case, the tissue was rather the fibro-cellular, as has 
been already explained (p. 18.) ; in the latter, they are appa- 
rently of an intermediate nature between the fibro-cellular 
and the vascular ; agreeing with the former in size, situation, 
and general appearance, but differing in being capable of un- 
rolling. In the stem of Endogens, spiral vessels occur in the 
bundles of woody tissue that lie among its cellular substance ; 
in the leaves of some plants of this description they are found 
in such abundance, that, according to De la Chesnaye, as 
quoted by De Candolle, they are collected in handfuls in some 
islands of the West Indies for tinder. The same author in- 
forms us that about a drachm and a half is yielded by every 
plantain, and that the fibres may be employed either in the 
manufacture of a sort of down, or may be spun into thread. 
In Coniferous plants they are few and very small, and in 
Flowerless plants they are for the most part altogether absent ; 
the only exceptions being in Ferns and Lycopodiaceae, orders 
occupying a sort of middle place between flowering and 
flowerless plants : in these they no doubt exist. My friend, 
Mr. Griffith, has succeeded in unrolling them in the young 
shoots of Lycopodium denticulatum, and Mr. Quekett in 
Diplagium seramporense. 
