CHAP. I> 
VASCULAR TISSUE. 
27. 
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. 11.) ; 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 vmrolling them in the young 
shoots of Lycopodium denticulatum. 
Some have thought that the spiral vessels terminate in those 
little openings of the cuticle called stomates ; but there does 
not seem to be any foundation for this opinion. 
Ducts {fig. 8, 9, 10, 11.) [Fausses trachees, Fr. ; Lym- 
phceducts^ or Sap-vessels of Grew and others ; Vaisseaux lym- 
phatiques of De Candolle, Vaisseaux pneumatiques of others) 
are membranous tubes, with conical or rounded extremities ; 
their sides being marked with transverse lines, or rings, or 
bars, and being incapable of unrolling without breaking. 
These approach so nearly to the spiral vessel that it is im- 
possible to doubt their being a mere modification of it. Some 
writers confound all the forms under the common name of 
spiral vessels, but it is more convenient to consider them as 
distinct, not only on account of their peculiar appearances, but 
