334 
Ruth Holden. 
ON THE RELATION BETWEEN CYCADITES 
AND PSEUDOCYCAS. 
By Ruth Holden. 
European Fellow of American Association of Collegiate Alumna. 
[With Plate III and One Figure in the Text.] 
ITHIN the last few decades, a great amount of work has 
been done in the endeavour to work out the relationships 
of fossil Cycads. It has proved an extremely arduous undertaking, 
owing chiefly to the scarcity of anatomically preserved material. 
This is true especially of leaves, where the criteria used in classifi¬ 
cation are necessarily based on the external features perpetuated 
by impressions. Recently, however, numerous additions have been 
made to our knowledge of fossil plants through the improved 
technique of the eminent Swedish palaeobotanist Nathorst. 
Nowhere has this work been more welcome than in its application to 
cycad fronds, and we may now hope that our classification will be 
based on features which are constant and trustworthy. As extended 
by Thomas and Bancroft (5) to the correlation of living and fossil 
material, we are now able to examine intelligently such minute 
structures as stomata, and to understand even the details of the 
thickenings of the guard cells. The importance of such work cannot 
be overestimated and it is very desirable that these new methods 
will be applied wherever possible. 
An interesting contribution by Nathorst (1) has been the 
establishment of the genus Pseudocycas for certain cycadean fronds 
formerly referred to the genus Cycadites. They differ from the 
latter genus in the possession of a double instead of a single midrib, 
and in the fact that the pinnules are not narrowed, but if anything 
broadened at the point of attachment to the rachis. The former 
character is not invariable, for Pseudocycas Steenstrupi has always, 
and P.insignis at times, only a single midrib—a discrepancy which 
Nathorst explains by suggesting that the two veins may sometimes 
fuse. Further, the stomata of the new genus are confined to the 
ridges formed by the double midrib and to the furrow between ; the 
epidermal cells are in long rows, and their walls are sinuous. 
Unfortunately the cuticle of an undoubted Cycadites has never been 
described, but assuming it to be like the living genus Cycas, it is 
evident that these constitute further points of difference, since the 
