456 Bower . — Studies in the Phytogeny of the Filicales . 
In 1 the leaf-trace appears as a projecting thinner part of the soleno- 
stele showing already the crinkled outline characteristic of the leaf-trace. 
Opposite it is a broad vascular strap — the compensation tongue. Two 
other leaf-traces (b, c) are already indicated by thinner regions of the ring. 
The medullary system consists of several strands of various size, disposed 
roughly in a ring, two lying irregularly near to the centre. In Text-fig. A, 2, 
the compensation tongue has fused at its margins with the incurved sides of 
the foliar gap, while processes which will form the hooks of the leaf-trace 
point inwards into the space thus enclosed. The medullary strands are 
disposing themselves in a circle with a central strand. This arrangement 
becomes clearer in 3 and 4, which also show the final separation of 
the leaf-trace (3), and of the petiole itself (4). Meanwhile, the traces 
b and c have become more definite, and in 5 the trace b appears as 
a thinner region strongly arching outwards. Opposite the gap thus 
forming, the broad compensation tongue already recognizable in 3 and 
4 is moving outwards to the gap. In 6 , 7, and 8 the stages already 
followed above for the trace a are repeated, with the same result. It is to 
be noted that already in 8 the compensation tongue for the leaf-gap c 
has been formed from the medullary system. From these drawings the 
plan of the vascular system of the shoot is sufficiently indicated. It is 
polycyclic, the outermost cycle being a closed solenostele: the middle 
cycle is somewhat irregular, but is fairly constant, with its connexion out- 
wards at each leaf-gap with the solenostele. Centrally is a simple strand 
of rather irregular position, which appears to connect with the middle cycle 
