260 PRINCIPLES OF BOTANY, ETC. 
last; the lymphatics with the pores of the cutis in 
the epidermis. In many plants of this kind this 
circle of vessels is closely pressed towards the centre, 
and the cellular texture very succulent and fleshy. 
But we never meet with more than one vascular 
circle, as there is annually a new one produced, as_ 
we shall soon see. For as the duration of the first 
is only that of a year, or a few months, the new 
circle cannot attach itself round the older. One 
exception to this we have in the beet, (Beta vulgaris), 
which is a biennial plant; its root, when about a 
year old, has from five to eight of these vascular 
circles. It follows, therefore, that beets produce 
them more then once, and they make an’ exception 
to the common rule, worthy the notice of physio- 
logists. oak | 
6 254... 
Perennial plants, which have no bulbs, or tuberous 
or creeping roots, are provided with a more or less 
conspicuous tube of pith, round which the addu- 
cent and air vessels form 4 circle, which is inclosed 
by avery firm’ cellular texture, ‘surrounded by the 
external integuments. “Every year a new circle’ is 
added, by the number of which we can always de- 
termine their age. ‘This is different in the creeping, 
tuberous and firm bulbous roots. They have, ac- 
cording to ‘their spéciesy their vessels in a circle 
closer to the centre, ‘or moré or less distant from it. 
They are annually renewed, and the old ‘ones die. 
On this account we find in most of them, fora few 
live more than one year, only one circle. 
Bulbs, 
