GARDENING AS A SCIENCE. 
131 
thrown doubt upon the opinion we then formed from observing that the elas- 
ticity of the spirals was prodigious — that they exist in one form or other in most 
plants — and that the peculiarity of their structure, which resembles the coiled 
spring of a bell- wire, argues that they have other functions allotted to them than 
that of merely conducting the sap. These and other properties, we stated, adding 
that the “ pliancy of trees, the readiness with which they yield to the force of 
winds, and the facility and springiness with which they recover their upright 
position, are facts strongly favouring the idea that they contain internal springs , 
which, like a coil of wire, are capable to receive and support motion in every 
direction, without offering impediment or receiving injury.” 
If these positions can be demonstrably controverted, the impugning facts ought 
to be stated ; if not, they may be considered as forming a part of the theory of 
vegetable function. 
As a further and general illustration, we observe that every member of the 
plant, including leaves, stipules, and bracts, comprises cellular tissue, abounding 
with fluid matter; that a system of fibres passes amidst these cells, traceable in 
the footstalks and veins of the leaf, &c. These fibres are manifestly the organs of 
support, which connect every member with the part where they ramify, and to 
which they are attached ; they also impart and sustain flexibility and motion. 
The cells, on the contrary, are the vehicles of fluids that pass and repass inter- 
changeably through the medium of that fine membrane which constitutes their 
walls ( parietes ). Can we then err, physiologically or chemically, in thus endea- 
vouring to assign peculiar, specific functions to organs so differently constructed ? 
Medullary , or Convergent processes . — In texture these rays are cellular ; in 
this all are agreed. Keith says that they are soluble in fluid, therein differing from 
the ligneous or fibrous layers. In exogenous trees the convergent rays are 
traceable from a very early period, but in herbaceous plants they are rarely 
seen till the plants produce seed. Du Hamel conceived that they originated in 
the pith, radiating as they advanced towards the bark, and hence were called 
divergent rays ; but Knight, while tracing the results of budding, observed that 
“the wood formed under the bark of the inserted bud unites, indeed, confusedly 
with the stock, though still possessing the character and properties of the wood 
from which it was taken, and exhibiting layers of new formation which originate 
evidently in the harlc, and terminate at the line of union between the graft 
and stock.” 
Again, Knight observed that if a portion of a stem be stripped of bark, so as 
to leave the surface of a small portion of the sap-wood (alburnum) uncovered, the 
wound will heal, “ first by means of the production of new bark issuing from the 
edges, and gradually narrowing the extent of the wound ; and then by the 
production of new layers of wood , formed under the bark as before. The new 
wood will not indeed unite with the portion of alburnum that had been exposed 
to the air ; but it will exhibit, on an horizontal section, the same traces of divergent 
