402 
VASCULAR CRYPTOGAMS. 
having the characteristic folding, but in the Equisetaceae it is the last layer but 
one of the cortical tissue which presents this appearance, whilst the innermost 
layer which directly abuts upon the axial cylinder seems to supply the place of 
the pericambium which does not exist in the roots of these plants. This innermost 
layer differs from the pericambium of the roots of other Vascular Cryptogams in 
that the lateral roots take origin from it, so that here also, as in all other Vascular 
Cryptogams, the lateral roots arise from the innermost layer of the cortical tissue. 
As a pericambium is wanting here, the commencing roots arise in immediate 
proximity to the external vessels of the axial cylinder. The cells, each one of 
which gives rise to a lateral root, are formed in strictly acropetal succession in 
the innermost cortical layer on the outer side of the primary xylem-vessels \ 
The Sporangia of Equisetacese are outgrowths of peculiarly metamorphosed 
leaves which are generally formed in numerous whorls at the summit of ordinary 
Fig. 284 — Diagram of the succession of cell-divisions in the apex of the root of Equisetum hiemale (after Nägeli and 
Leitgeb), (this diagram will serve also in the main for Ferns and for Marsilia). A longitudinal section ; B transverse section at 
the lower end oi A ; h h h the primary walls, j j .r the sextant walls of the segments, indicated in A by the figs. / — XVI, 
k I m n p the layers of the root-cap, all the further divisions being omitted \ c c\Vi the interior of the root indicates the walls by 
which the rudimentary fibro-vascular cylinder (procambium) is divided from the cortex of the root, e the boundary-wall between 
the epidermis o and the cortex (epidermal wall), r r boundary-wall between the outer and inner cortex (cortical wall), i, 2, 3, the 
successive tangential walls by which the inner cortex is divided into several layers, the radial divisions being omitted. 
shoots or of those specially destined for this purpose. Above the last sterile leaf- 
sheath of the fertile axis an imperfectly developed leaf-sheath is first of all produced 
(Fig. 285, ^z), a structure corresponding in some degree to the bracts of Phanerogams. 
The development of this structure is sometimes more, sometimes less leaf-Hke ; foliar 
girdles are formed above it in acropetal succession beneath the growing end of 
the shoot, projecting however but slightly, as in the ordinary formation of leaves 
of Equisetum. A large number of protuberances project from each of these girdles, 
corresponding to the teeth of the ordinary leaf-sheaths ; and thus several whorls of 
hemispherical projections are formed lying closely one over another, which, in- 
creasing more rapidly in size at their outer part, press against one another, and 
thus become hexagonal, the successive whorls alternating; while the basal (inner) 
A 
^ [See Van Tieghem, La Racine, Paris 187 1.] 
