130 
GARDENING AS A SCIENCE. 
water only can be safely affirmed to pass into the roots ; and yet as manures 
become decomposed within the soil, it is reasonable to conclude that the elements 
of water, combined with some hydro-carbon, enter, and thus furnish the plant with 
certain portions of its constituent elements. Again, we may reason thus — a plant 
deprived of its roots must inevitably perish, and if it be not properly supplied with 
some appropriate manure, although it may continue to exist, it ceases to flourish, 
its foliage and green parts become degraded, and a premature bloom is frequently 
produced ; it therefore obtains carbon in one form or other. 
The Sap of a Vine prior to the development of its full foliage can be collected 
at two periods of the day. In taste it is nearly insipid, yet while drying upon the 
wounded shoot, it deposits a considerable quantity of salt of lime. Prout has 
given a complicated statement of its components ; but we prefer to abide by what 
we have witnessed ; and as it appeared that by the addition of oxalate of ammonia, 
a milkiness, followed by a sediment, was produced, we obtain further evidence 
that vine-sap contains lime in solution. As therefore lime is an inorganic product, 
is often present in soil, but never in the air, it must be inferred that, in common 
with other inorganic constituents, it is introduced with the aqueous sap derived 
from the earth. 
The conduits of the crude sap were supposed to be tubes, and in some of the 
tubes (longitudinal vessels) of purely herbaceous subjects, or very young wood, 
fluid can be traced ; but the cellular tissue is always replete with juices, and there- 
fore it should appear that Mr. Knight was perfectly correct in his opinion, that it 
is through the medium of the cells that the sap ascends. It had been observed, 
that the fibres were very numerous and strong, that they ran longitudinally, and 
with great uniformity, together. But in these woody fibres no trace of perforation 
anything resembling tubular structure could be discovered. However, it was 
necessary to believe that sap-vessels must exist somewhere, and certain writers, 
overlooking the system of juicy cells which surround and clothe the woody and 
threadlike fibres, advocated hypotheses all difi*ering from' each other, but none 
approaching in luminous simplicity to the cellular theory of Mr. Knight. 
The fibrous^ or, as some call it, the tubular system, appears then to be the 
representative of bone in the animal economy ; for, by degrees the fibres consoli- 
date, and become wood in trees, and substance equivalent to wood in the softer 
and herbaceous tribes ; they are the framework of vegetable structure, and not the 
permanent vehicles of fluid nutriment. But what shall be said of those interesting 
pieces of refined mechanism, the spirals f 
These have been defined by some as accessories to the sap-vessels. Others view 
them as air-tubes, on the ground " that there appears to be no provision for the 
conveyance of air through the central parts of plants, if that office be not performed 
by the spiral vessels." 
Many years since we suggested that the spiral system might act as the organ of 
elasticity ; and nothing has occurred or been written which has, in any degree, 
