The Structure and Origin of the Cycadaceae. 
BY 
W. C. WORSDELL. 
With seventeen Figures in the Text. 
N O family of plants is exciting more interest at the present day than 
the Cycadaceae, and this for the prime reason that they represent 
one of those forms of plant-life which link the types of the far past with 
those of the present modem world. They are placed to-day at the lowest 
levei of the great Gymnosperm-class, but they possess certain peculiarities 
of habit, external morphology, and anatomical structure which undoubtedly 
suggest an affinity between them and that large group of the Vascular 
Cryptogams, the Ferns. The majority of authors who have written on the 
subject are at one on this broad question of Filicinean relationship. 
They begin to differ from one another, however, when considering more 
in detail the group or groups of Fern-like plants to which our modern 
Cycads are related or from which they have been derived, and also the 
lines along which the descent with modification has apparently taken 
place. 
The group of Fern-like plants from which our modern Cycads are 
probably derived is that termed by Potoni£ the Cycadofilices, but more 
recently named by Scott and Oliver, Pteridospermeae, itself probably 
representing a transitional stage of evolution between the Ferns proper and 
modern Cycads. 
Having been asked to contribute a resume of my views as to the origin 
of Cycads from the Pteridosperms (views which have been founded chiefly 
on facts of their vascular anatomy), the following account is written in 
compliance with that request. 
The Habit and Structure of Cycads. 
I will first give a brief description of the characters of the Cycadaceae. 
The Tree-fern-like habit of these plants is the first thing to be 
remarked ; the thick stem often coated externally with an armour-plate 
of old leaf-bases, bears at its summit a crown of large fronds ; but here 
[Annals of Botany, Vol. XX. No. LXXVIII. April, 1906.] 
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