106 
Osborne^ on the Wheat Plant. 
come the roots (PI. Ill, fig. 1). If this exuded white sub- 
stance is examined at this stage_, it will be found to consist of 
several layers of cell-texture. The outer one has ceUs with 
extremely thin walls ; their length is far greater than their 
breadth, and very often they have no visible contents. The 
few next layers consist of thick-walled, angular cells, very full 
of granular matter. We then find smaller cells of the same 
form, the contents granular, but of a darker colour, with 
large nuclei occupying the greater proportion of each cell. 
We now come to the vascular bundle. This consists of tubes 
of scalariform,"^ or pitted fibre ; I use the term tubes for 
want of a better, but I am satisfied that these long cells, with 
their barred and dotted fibre, are not hollow in the true 
sense of the word. They are firmly held in position by being 
placed within a mass of simple cellular tissue, which makes 
up with them the structure I have called ^^the vascular 
bundle." In the centre of this bundle, and passing throughout 
its entire course, are one or more tubes. I assume them to 
be channels for the sap ; when dissected out they give, in a 
vertical view, two parallel lines of some hyaline substance, 
united by a highly transparent membrane, and enclosing 
granular matter. 
A transverse section of one of these sap-tubes, made at the 
base of a root (PI. Ill, fig. 2), shows two kidney-shaped out- 
lines, enclosing in the space formed by their concavity a circular 
space, very similar in appearance to one of the nuclei found in 
cells. These bundles of fibre, with their investing layers of 
cells, are connected with the germinating point of the seed, by 
thick-walled, cellular texture (fig. 3), the spaces or cells being 
very full of a dark granular matter, in which globules of some 
oleaginous substance may be made out. The immediate con- 
nection of the epidermis of the plumule with that of the 
roots, is also a space of cellular texture, the cells of which, 
when divided vertically, are found to have their walls formed 
in minute cavities. The only idea I can give of a section of 
one of these cells is that of a series of pipes which have been 
bent into circles, laid upon one another, cemented together, 
and then a vertical section made through them, so as to 
expose their several inner faces. I find that cells of a very 
similar structure to these, will in the end assume the cha- 
racter of annular fibre, [Vide note at the end.) 
The cones of protruded substance of which I have spoken 
soon burst their outer coat of cell- texture. At this early stage 
a root cone, if dissected out and placed under the sixth object- 
* I use the word scalariform simply to mark the character of that species 
of vessel which has a ladder-like appearance. 
