DISTRIBUTION AND RELATIONSHIPS OF THE CYCADEOIDS 
Bearing in mind, then, these greatest of all problems of plant history, 
many of the genera so difficult to place could be cited. A few may suffice. 
Podozamites lies on the cycadeoid-conifer boundary. Brachyphyllum stems 
must approach in structure as well as in appearance the cycadeoid stem 
types. But yet, by constant and consistent attention to main phases of 
the fossil plant alignment, and by continual revision of the percentual 
record of occurrence, the general nature of the forward movement of 
cycadeous plants can undoubtedly be brought out. It is very interesting 
indeed to find that in the Australian Rhaetic and Lias the proportions of the 
several plant phyla are in harmony with those noted elsewhere. In fact, 
there are certain features of Mesozoic vegetation which stand out as very 
important, and which could not be discerned without the aid of this per- 
centual method. It displays the great abundance of the Pterophyllums 
at the earlier end of the cycadeoid record. Also, the Taeniopterids which 
are separated from the other forms by A. B. Walkom in his Australian 
studies, as they should be, are a singularly prevalent type in the late Triassic. 
They are often small-leaved, and if largely cycadeoid they are of course the 
forms which stood very close to the leaf types leading toward the dogbanes, 
the oleanders, and the Magnolias. In the Lias, where climatic variation is 
suspected, the stereotyped pinnate fronds of the tropics (Oaxaca) mark the 
culmination of plants apparently cycadeoid. 
As an example of distribution and relative abundance expressed per- 
centually, the subjoined table (table i) from Walkom may be scanned. 
It displays the relations found in the plants of the "Ipswich series" of the 
lower Mesozoic rocks of Queensland, Australia. 
Table i. 
No. of Species 
Equisetales 
Filicales 
Filicales (incertae sedis) 
Taeniopteris 
Cycadophyta 
Ginkgoales 
Total 
15 
30) 
:I1 
15 
57 
15 
39 
24 
33 
Such tables are certainly helpful, with the fossils actually in hand. And 
their graphic value can scarcely be denied. As Walkom observes, ''they 
must be used with a good deal of caution, lest they lead to quite incorrect 
and even absurd results; although with a full realization of their value 
and also their drawbacks, they may yield interesting and to some extent 
reliable results." Note that the Equisetales suggest a Triassic abundance, 
while the considerable number of Filicales, with a large (early) gymnosperm 
series, is in accord. The general description of the flora given by Walkom 
sustains his conclusion that these plants may be of upper Triassic (or 
