EQUISETINEM. 
401 
to the light. It may be assumed that there is always as large a number of buds 
in a rudimentary condition as there are sheath-teeth. On the erect leafy stems 
of E. Telmateia, E. arvense, and other species, they all attain complete development, 
and produce the numerous slender green leafy shoots of these species ; in other 
species the development of the branches is more sparing; some, as E. Memale, 
usually form no aerial lateral shoots at all except when the terminal bud of the 
stem is injured, and then the node next below produces a shoot. Branches do 
not usually make their appearance on rhizomes in the form of complete whorls, 
but in twos or threes, but on the other 
hand they are more vigorous ; they be- 
come either new rhizomes or ascending 
stems. Since, in the cases first mentioned, 
the buds arise like the leaves in strict 
acropetal succession, it may be assumed 
that where the production of shoots is only 
induced at a later period by accidental 
circumstances, the buds have up to that 
time remained dormant in the interior. 
The Roots arise in whorls, each im- 
mediately below a bud ; but they may also 
often be suppressed, and may be deve- 
loped, according to Duval-Jouve, even on 
aerial nodes, by humidity and darkness. 
Their development has been studied by 
Nägeli and Leitgeb (/. c.) ; in its earliest 
stages, which are represented diagram- 
matically in Fig. 284, it resembles essen- 
tially that of Ferns. The cortex is differ- 
entiated into an inner and an outer layer ; 
the former forms air-conducting intercel- 
lular spaces, at first arranged, like the cells 
themselves, in radial and concentric rows, 
and afterwards combining by the rupture 
of the cells into a large air-cavity sur- 
rounding the central fibro-vascular cylinder. 
As the fibro-vascular cylinder of the root 
developes (seen in transverse section), 
each of the three primary cells which 
alone of the six reach the centre is first of all divided by a tangential wall, so that 
the rudiment of the vascular bundle now consists of three inner and six outer cells. 
The six outer cells produce a carnbial tissue in which the formation of vessels 
begins, commencing from two or three points of the circumference and advancing 
towards the interior. Last of all one of the three inner cells forms a broad central 
vessel ; and phloem is produced in the circumference of the vascular cylinder. In 
the other vascular Cryptogams the innermost layer of the cortical tissue forms 
the bundle- sheath {Pkromscheide^ Schuizscheide), the radial walls of the cells 
D d 
Fig. 283. — Longitudinal section through an underground 
bud oi Eqicisetunt arvense; ss apical cell of the stem, b—gb the 
leaves; K K' two buds; the horizontal lines across the stenx 
indicate the position of the diaphragms. 
