HEW PHYTOhOGIST. 
Vol. VI., No. 8. 
Oct. 3 i st, 1907 . 
LECTURES ON THE EVOLUTION OF THE 
FILICINEAN VASCULAR SYSTEM. 1 
By A. G. Tansley, M.A. 
(University Lecturer in Botany, Cambridge). 
LECTURE VI. 
The Evolution of Dictyostely. Polycycly. 2 
[Figs. 51—64.] 
If we start from the condition of solenostely (Fig. 51) and 
consider the evolution of dictyostely (Fig. 52), we realise at once 
that as soon as two successive leaf-gaps overlap, either by crowding 
of the leaf-insertions, or by the prolongation forward of each leaf- 
gap till it passes the base of the next trace, the stele technically 
ceases to be a solenostele on Gwynne-Vaughan’s definition (p. 152), 
A 
Fig. 51. Solenosteles, nodal portions, seen from dorsal side of rhizome, 
showing leaf-gaps and bases of leaf-traces. A. Dennstcedtia punctiloba. 
B. Microlcpia speluncce. After Gwynne-Vaughan. 
and becomes a simple dictyostele, 3 defined as an amphiphloic cylinder 
in which at least some transverse sections show two or more leaf- 
gaps. 
1 A Course of Advanced Lectures in Botany given for the 
University of London at University College in the Lent 
Term, 1907. 
2 The present lecture is largely based on the work of Gwynne- 
Vaughan (’03). 
3 Brebner (’02). 
