232 
F. W. Oliver. 
PTERIDOSPERMS AND ANGIOSPERMS. 1 
By F. W. Oliver. 
[With Text-Fig. 32]. 
NE of the great outstanding problems of Morphology now 
engaging the attention of Botanists is that of the origin of 
the dominant class—the horde of plants of complex organisation 
known as the Angiosperms. The revival of active interest in this 
question may be traced partly to the application of fresh methods 
to its solution, partly to the advance in knowledge of the less highly 
organised groups from among which the Angiosperms may have 
sprung. During the last few years Paleobotany has not been idle, 
and it is more particularly the relation of additions in this field to 
the Angiospermic question that will be considered in the present 
article. 
Among these additions are two especially deserving of attention. 
First there is the material expansion in our knowledge of the 
Mesozoic Cycadophyta now focussed in Wieland’s notable contri¬ 
bution on “ American Fossil Cycads ” 2 ; secondly, there is the rapid 
re-arrangement of our ideas of the status of the fern-like plants of 
the Palaeozoic, a re-arrangement from which emerges a class of 
generalised spermophytes, the Pteridospermeae. 
These additions, which practically effect a change in the 
situation, make it necessary to consider once more what ground we 
have for the encouragement of the hope that some day it may be 
possible to link up the Angiosperms with the main series of vascular 
plants. 
It will be convenient at the outset to glance at the chart (fig. 
32) which represents in rude enough fashion the distribution in time 
of the great classes of vascular plants. A striking general feature 
(brought out by the shading employed) is the relative abundance 
and antiquity of the Spermophytes in the fossiliferous rocks, a pre¬ 
dominance which serves to emphasize the incompleteness of the 
records as compared with the whole scheme of plant-evolution. 
Turning to the several epochs, the great feature of the 
Cainozoic is the rapid expansion of the Angiosperms, which, 
starting in Cretaceous times, soon rise to overwhelming dominance. 
The origin of this great group remains an unsolved mystery, for it 
can hardly be maintained that the supposed “ Pro-Angiosperms” of 
1 Being the substance of a Paper read before the Botanical Club, 
Cambridge, December 4th, 1906. 
3 See Review, p. 242. 
