Polycycly. 199 
the leaf-gap in the outer cylinder and also supplies the abaxially 
directed limbs of the trace on each side (U). Eventually the 
trace undergoes a final complication, the abaxially directed limbs 
being again curled inwards, so that their free edges are now directed 
adaxially (V and Y). To meet this complication the second cylinder 
now sends up a double branch on each side, so that both the limbs 
of each lateral loop are supplied by the internal cylinder. As the 
diameter of the whole stele increases the second cylinder, instead 
of sending up the column of tissue shewn in Fig. 61, U, gradually 
Fig. 61. Continuation of Fig. 60, drawn to a scale one-third that of Fig. 
60. In T to Y the outlines only of the vascular cylinders are drawn. 
raises its roof towards the node, so that it comes into bodily contact 
with, and thus supplies the lateral loops of the leaf-trace on each 
side, while a tongue of tissue passes forwards and upwards, as in 
Pteris data , to fill the gap in the outer cylinder. The free edges of 
the outer limbs of the lateral loop on each side are continued down¬ 
wards and forwards as upstanding flanges (X,_/Z) along the edges of 
