Botryopteris antiqua , Kidston. io 55 
leaf-traces, both monarch and diarch, has been traced in detail The 
preservation of the phloem elements is unsatisfactory, but indications of the 
characteristic large sieve tubes seen in later species can be made out 
surrounding the xylem of the petiolar bundle. 
Reasons are adduced against the theory that the Botryopteris type of 
petiole is derived from the Anac horopter is type. 
XL Conclusion and Acknowledgements. 
I have had the privilege of discussing the problem of the aphlebiae 
with Dr. D. H. Scott. 
All the slides were cut and, with two exceptions, all the micrographs 
taken by C. H. Wells, my laboratory attendant. 
Help towards the expenses of the work was received from the Royal 
Society Government Grant. 
The boulder from which the sections shown in Figs. 16, 22, 24, and 
25 were cut was kindly presented to me by Professor I. B. Balfour. 
EXPLANATION OF PLATES LXXXI-LXXXIII. 
Illustrating Dr. Margaret Benson’s paper on Botryopteris antiqua. 
Abbreviations used: aph. = aphlebia, c. — cusp limiting the protoxylem group of a leaf-trace, 
m l.t. = monarch leaf-trace, d.l.t. = diarch leaf-trace, p.s . = pseudo-secondary thickening, px. — 
protoxylem, r. = root, s.s. = stem stele. 
All the figures are photomicrographs from slides in the Royal Holloway College Collection. 
PLATE LXXXI. 
(Figs. 1-9.) 
Figs. 1-5 represent successive transverse sections through a stem stele. Slides 407. 12-8. 
Fig. 1 shows the condition of the stele in a leaf-bearing zone immediately after the liberation 
of a diarch trace. The single protoxylem (px.) is about to bifurcate. Slide 407. 12. x 95. 
Fig. 1 a is a low-power micrograph of the whole section from which Fig. 1 was taken, x 20. 
Fig. 2 shows the completed duplication of the protoxylem (px . 7 px .') shown in Fig. 1. 
Slide 407. 11. x 95. 
Fig. 3. The next leaf-trace ( m.t.t .) is preparing to leave the stem stele. Slide 407. 10. x 95. 
Fig. 4. The leaf-trace shown in the stem stele in Figs. 2 and 3 has now just become 
free ( m.l.t .). The stem stele is rapidly increasing in size by pseudo-secondary thickening (p.s.). 
Slide 407. 9. x 95. 
Fig. 4 a is a low-power micrograph of the whole section from which Fig. 4 was taken. It 
shows both the leaf-traces still in the cortex, x 20. 
Fig. 5 is a low-power micrograph of the next section of the same series, showing the two 
petioles supplied by the above traces just leaving the stem. Slide 407. 8. x 20. 
Fig. 6. A micrograph of a stem giving off a root and a leaf-trace. The stem stele which 
shows an early stage in the liberation of another trace is shown enlarged in Fig. IV a. Slide 
405. 16. x 20. 
Fig. 6 a. An enlarged view of the stem stele shown in Fig. 6. The protoxylem of the leai- 
trace appears to be dividing (cp. a corresponding stage in the protoxylem of the stem in Fig. 1). 
3 z 2 
