Polycycly. 
229 
arise from the external and lateral faces of the cauline meristeles, 
one invariably from the point where the internal strand fuses with a 
meristele of the ring, so that a direct water channel exists between 
this root and the next leaf above. 
Two strands only are given off to supply the petiole. As they 
pass outwards they divide into several (eight or nine) separate 
strands, which are arranged, in the base of the petiole, in a typical 
horseshoe-shaped curve (Fig. 72). The terminal strands of the 
curve advance towards the median (vertical) plane of the petiole, 
and at one point in the pulvinus they fuse to form a single broad 
strand, the protoxylems of which face abaxially (Fig. 72, A). 
Higher up they become separate again, and curving gradually 
inwards, they rotate at the same time, so that their protoxylems 
(endarch) come to face towards the sides of the petiole (B and C). 
Internal accessory strands, quite distinct from those of the primary 
curve, and having no connexion with the internal strands of the 
stem-cylinder, occur in the pulvinus at the base of the petiole. Two 
of these arise as internal branches of the abaxial strands of the 
primary curve, fuse together, separate again (A), and travel slowly 
across the internal ground tissue, to fuse with the two terminal 
strands of the primary curve (B). These internal strands, not 
belonging to the primary vascular curve of the petiole, are found in 
all the genera of Marattiaceae, and are one of the characters 
separating this group from other Ferns. 
Fig. 73. Domra siviplicifolia. Transverse sections of solenostele of 
young plant, showing passage of internal accessory strand (/.s.) across pith; 
l.t., leaf-traces ; l.g., leaf-gap ; li., roots. From Brebner. 
