ADHESIVE DISCS OF ERCILLA VOLUBILIS. 97 
cells. These eventually become the connexion between the 
vascular tissue of the dise and that of the stem (fig. B). By 
irregular divisions and inerease in length, similar elongated cells 
are formed in a plane at right angles to the connecting cells, 
thus forming a flattened plate running through the projection 
in all direetions in a plane parallel to its free surface (fig. 4). 
These elongated cells are, for the most part, gradually differ- 
entiated into tracheides with scalariform thickenings. The vas- 
cular plate thus formed is thicker towards the centre, becoming 
thinner as the periphery of the projection is reached. The 
vascular tissue of the dise is thus connected with that of the 
stem at a point above the axillary bud, where a plexus is formed 
abutting on the lignified pith-cells, previously described (fig. 4). 
The cells immediately above and below the vascular plate of the 
dise meanwhile continue to divide and increase in size. The 
resulting pressure from within ultimately effects the rupture of 
the epidermal layer, which thus is broken up, and eventually 
becomes exfoliated. The central eclumnar cells elongate rapidly, 
and, after the disappearance of the epidermis, they develop into 
hairs. The formation of hairs spreads from the central position 
gradually over the whole surface of the dise, thus completing 
the disruption of the epidermis, some of the cells of which are 
carried up on the apices of the hairs (see Pl. 5. fig. 5, e). This 
kind of subepidermal origin of hairs is unusual * ; for example, 
in the “ suckers ” of Ampelopsis t, which have several points in 
common with the dises of Ercilla, the hairs spring from the 
epidermis alone, and not from a definite layer previously laid 
down beneath it. 
PN this point the dise be in contact with a wall or other 
ness and e the whole organ increases in area and thick- 
coming in e ams grow to considerable length. The latter, 
contact with the wall, adhere to it, in the first instance 
* Some time 
Journal de Bota 
mique des poil 
formation of 
after this paper was sent in, Van Tieghem published in ‘Le 
nique" (February Ist, 1897) a paper entitled “ Origine exoder- 
S post-staminaux des sópals chez les Santalacées,” in which the 
of the cpidermin d from a subepidermal layer, and the consequent exfoliation 
to that described Lambe. The development appears to be precisely similar 
similar sube ide a ove for the hairs of the discs of Ercilla. Hitherto no 
Cites the case of n origin of hairs has been observed, and Van Tieghem 
“von Len ee as unique in this respect. (n 
Arten der Gatt DU Die Bildung der Haftballen an den Ranken einiger 
ung Ampelopsis.” Bot. Zeit. 1885. 
LINN, Jo 
URN, —BOTANY, VOL. XXXIII. H 
