62 THE VEGETABLE WORLD. 
are only small rudimentary scales, at whose axils the branches, 
which extend themselves more or less horizontally, develop them- 
selves, and are charged with abortive leaves. These branches, 
which are thin and slender at their origin, swell at their extremities, 
are filled with a green pulverulent matter, and finally become the 
tuber, which we recognise as the potato. In short, if we examine 
a potato, we see that it is covered at intervals with eyes, or scales. 
At the axils of these scales a bud is found ; every one knows that 
these buds, when the potato is stored in dark cellars, push out 
long slender shoots at the return of spring. These are their true 
branches or stems. The fact that the parts here described are — 
really portions of the stem, is curiously proved by the following 
instance recorded in the Gardener’s Chronicle, vol. ii. p. 89 
A potato plant had grown underneath an inverted flower-pot in a 
dark cellar, where it had formed itself into a perfect miniature potato _ 
plant. Being only surrounded by air, it had thrown out its 
branches, and meeting with no resistance, it had grown with the ‘ 
same regularity as an ordinary plant would have done above — 
ground. The set, or old tuber, was shrivelled up, and formed a 
wrinkled knob, out of which grew many branches and branchlets. 4 
Of the latter, some had become thickened at the point, resembling 
young potatoes ; others, having no power of extending themselves, q 
had swelled close to the parent tuber. All wore covered scales, — 
the rudiments of leaves. At first sight the plant appeared as if 4 
’ 
it had been unable to form roots, but a more minute inspection : : 
showed that they were really beginning to form here and there 10 
many places upon the surface of the branches. 
q 
There is a great difference between tubers—between the Potato 
and the Dahlia, for instance. The tubercule of the Dahlia may be 
called a true root; it has no vital node, or joint. On the other — 
hand, the stem of the potato bears many of these vital knots. 
The length and direction of the branches, as compared with the 
parent stem, are extremely varied, and this variety tends to give 
to each plant its special appearance, its peculiar physiognomy. If 
the lower, and consequently first formed branches, continue 0 
extend themselves in the same proportion, and the upper ones 
are shorter as they approach the summit, the form of the tree i8 
‘conicalor pyramidal, as in the Firs (Fig.76). If the central branches 
