GARDENING AS A SCIENCE. 
107 
to offer any remark upon the functions of organs ; their actual existence and 
structure requiring to be proved before we have any just pretension to define their 
offices. That tlie microscope can, and does detect variations, there can be little 
doubt. The true spiral may be observed by the aid of one of Ross's single 
botanical microscopes ; and, indeed, its coils will be seen by the unassisted eye. 
The following passage, from a later Treatise by the same society, may conduce to 
some very gratifying investigations. 
" Spiral vessels are generally seen by learners in an unrolled state, which is the 
most easy to obtain, but the worst calculated to give a correct idea of their real 
nature. One of the best modes of seeing them is to take a piece of asparagus as 
it is brought to° table, and to tear it to pieces in water. By means of a little 
tearing and cleaning, you may extract from the pulp, — which is cellular tissue, — a 
quantity of fibrous bundles, which are in part woody fibre, and in part spiral 
vessels ; the elasticity and disposition to unroll, in the latter, being destroyed by 
the boiling, they may be easily separated in an entire state, when the true 
position of their internal fibre will be distinctly perceived." 
The experiment is easy, but the expression, internal Jihre, requires observation. 
The true spiral tube — if we mistake not— is composed entirely of a fine, closely- 
compressed coil of membranous thread ; the elasticity of which is, doubtless, lost 
by boiling ; — but the expression, internal fibre, implies that the coil itself is 
inclosed by a tube, of which it forms a subsidiary member. Now there are tubes 
or vessels, so composed, and these constitute the reticulated, and punctuated ducts. 
Microscopes of excessively high power, those through which light passes, and 
transfers the object to a screen, may, perhaps, ultimately lead to some correct disco- 
veries ; but, in the present state of knowledge, the student, with such instruments as 
are usually at his own command, will find cause of hesitation at every step ; he will 
perceive optical delusions, appearances upon which he cannot satisfactorily confide ; 
yet we may venture to assert that, as respects the true spiral, the evidence will be 
decisive, that it is simple in its construction, though the spires may adhere together, 
and form a perfect tube till they become unrolled. 
The above have been considered as forming the system of vessels which conduct 
the ascending fluids ; Lindley names a series which is termed Laticiferous Tissue^ 
whose office is to convey a peculiar coloured fluid, called latex, to all the newly- 
formed vessels : they are identical with the proper vessels of the old writers. This 
tissue is confined to the liher, or inner bark of exogens chiefly ; it appears to be 
intermediate with the system of vessels which return the laborated fluids from the 
leaf back to the plant, and which, therefore, were called Reducent vessels. These 
constitute the simple tubes of Mirbel. 
The best theory we meet with, which, after all, amounts to little more than 
conjecture, is the following : — 
The returning vessels have their origin in the leaves ; the sap-vessels are closely 
accompanied by them in each rib of the leaf, but they separate in the foot-stalk at 
