CHAP. I. 
VASCULAR TISSUE. 
25 
end in conical spires, the point of which becomes very acute ; 
but one would not suppose, judging from the figure given by 
the latter writer, that he had seen the terminations very 
clearly. It is, however, certain that the statement of Nees 
von Esenbeck is correct, and that the spiral vessel generally 
terminates in a cone, or in a rounded manner. If the point 
of such a vessel in the Hyacinth (Plate II. fig. 9.) be examined, 
it will be seen that the end of the spiral fibre lies just within 
the acute point of the vessel, and that the spires become 
gradually more and more relaxed as they approach the ex- 
tremity, as if their power of extension gradually diminished, 
and the membrane acquired its pointed figure by the diminu- 
tion of elasticity and extensibility in the fibre. It is not, 
however, always in a distinct membrane that the spiral vessel 
ends. In Nepenthes the fibres terminate in a blunt cone, in 
which no membrane is discoverable. (Plate II. fig. 11.)* 
A spiral vessel is formed by the convolutions either of a 
single spire, or of many always turning in one direction, and 
forming a right-handed screw (Slack). In the first case it is 
called simple, in the latter compound. The simple is the most 
common. (Plate II. fig. 9.) Kieser finds from two to nine 
fibres in the Banana. De la Chesnaye as many as twenty-two 
in the same plant. There are four in Nepenthes. (Plate II. 
fig. 11.) In general, compound spiral vessels are thought to 
be almost confined to Endogenous plants, where they are very 
common in certain families, especially Marantaceae, Scitami- 
ne^e, and Musaceae ; but their existence in Nepenthes, and, 
according to Rudolphi, in Heracleum speciosum, renders it 
probable that future observations will show them to be not 
uncommon among Exogens also. 
* A singular change occurs in the appearance of the spiral vessels of 
Nepenthes, after long maceration in dilute nitric acid, or caustic potash : 
the extremities cease to be conical and spirally fibrous, but become little 
transparent oblong sacs, in which the spires of the fibres gradually lose 
themselves. This alteration, which is a very likely cause of deception, is 
perhaps owing to the extremities of the vessels being more soluble than the 
other part, the sac being the confluent dissolved fibres. This is in some 
measure confirmed by the subsequent disappearance of all trace of fibres 
in any part of the vessels, under the influence of those powerful solvents. 
