HEW PflYTOItOGIST. 
Vol. VI., No. io. 
D EC. 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 VIII. 
The Osmundace/E and Ophioglossales. 
[Figs. 81—95.] 
We have now completed our task of tracing the evolution of 
the vascular system in the Filicinean phylum from the simple 
protostelic forms found in the Hymenophyllaceae and Gleicheniaceae 
to the most complicated dictyostelic and polycyclic types such as 
we find in the most advanced Marattiaceae. 
In so doing we have omitted the consideration of two important 
families or groups (one undoubtedly Filicinean, and the other shewing 
several Filicinean features) because they stand rather apart from the 
main lines of anatomical evolution so characteristic of the great 
majority of the Ferns. To these we must now devote some attention. 
OSMUNDACEAi. 
Undoubted representatives of this very old family are known 
from the Jurassic and Rhastic, while certain Palaeozoic forms 
show a considerable resemblance to the family type. The 
Osmundaceae are now represented by two genera, and are distinctly 
isolated in several respects; in the development and structure 
of the sporangia, in the structure of the prothallus, and even 
more markedly in the anatomy of the stem. The sporangia 
stand closest to those of the Botryopterideae, and the structure of 
the vascular system of the stem in some existing forms recalls that 
’ A Course of Advanced Lectures in Botany given for the 
University of London at University College in the Lent 
Term, 1907. 
