HEW PHYTOLOGIST. 
Vol. VI., No. 5. 
May 31 st, M 907. 
LECTURES ON THE EVOLUTION OF THE 
FILICINEAN VASCULAR SYSTEM . 1 
By A. G. Tansley 
(Lecturer on Plant Anatomy at University College, London). 
III. —The Modern Ferns and Anatomical Evolution— 
The Hymenophyllace,e:. 
[Figs. 23—33]. 
We now turn to a consideration of the vascular system of the 
modern ferns, and in tracing its various modifications two alter¬ 
natives are open to us. We might on the one hand take first the 
most primitive families, as judged by soral and sporangial characters, 
and consider how far their vascular system corresponds in grade of 
evolution with their reproductive organs, gradually progressing to 
the families with the most highly developed sori and sporangia. If 
it were our task to review the ferns systematically from a general 
standpoint this would be the obvious course, but when we are 
dealing primarily with the evolution of the vascular system, there 
are good reasons for departing from it. On the whole there is a 
very striking parallelism between vascular and sporangial characters 
in the Leptosporangiate Ferns. Thus among the Simplices of 
Bower we have almost exclusively protostelic and solenostelic 
forms; the Gradatae include the protostelic Hymenophyllaceae, but 
are for the most part solenostelic; among the Mixtae are included 
the great mass of dictyostelic types, though with many solenostelic 
forms intermixed, and in the family of Lindsayeae we have a typical 
“mixed” sorus co-existing with a type of vascular cylinder inter¬ 
mediate between the protostelic and solenostelic conditions. We 
are perfectly safe in concluding that there has on the whole been 
1 A Course of Advanced Lectures in Botany given for the 
University of London at University College in the Lent 
Term, 1907. 
