72 SECTIONAL ADDRESSES 
like those that could be detected in different areas among the older suites 
of plants, cannot be seen—the associations from widely separated places 
are very similar ; and there is decidedly less difficulty in assigning speci- 
mens to their -proper botanical group. Plants of doubtful affinities are 
fewer. Thus lines of evolution can be traced, as, for example, in the 
Osmundacez and the Bennettitales. The last group has been of special 
interest, and the works of Dr. Wieland, Prof. Seward, Dr. Marie Stopes 
and Dr. H. H. Thomas have illustrated the wonderful variety of form 
included init. Indeed it might be called the distinctive group of Mesozoic 
times, though the Ginkgoales also constitute another very prominent 
group. 
The physical conditions under which some forms lived can sometimes 
be detected. The swamp flora can be seen in association with coals 
like the Brora coal, Eguisetites is a common type; the estuarine series in 
Yorkshire yield a flora that has drifted probably from lowland regions ; 
and the conifers and cycads illustrate plants from a rather drier, and 
possibly upland, environment. In this connexion the Portland and 
Purbeck beds are specially interesting to the geologist. Drifted stems 
of cycads, and logs of coniferous wood, are not uncommon in the Portland 
quarries ; but the curious rings of tufa deposited round erect stems, as 
seen at Lulworth, probably point to lagoonal conditions of slow subsi- 
dence and gentle laving of the stumps by waters rich in calcareous material. 
An explanation of the well-known breccia beds of that last-mentioned 
locality, as due to deposition over thick accumulations of plants that 
subsequently rotted and caused the over-lying strata to be broken up, need 
not detain us, except to express our doubt of the suggested solution. The 
water of these lagoons was frequently evaporated to dryness, as the 
conspicuous rock salt and gypsum pseudomorphs attest. ‘This is merely 
a local point of interest, but several of us here visited the area during the 
British Association meeting at Southampton, and it recalls to me pleasant 
memories of our discussion of the Jurassic flora on the spot. 
THE LOWER CRETACEOUS FLORA. 
The plants of the upper Jurassic beds are generally similar to those that 
occur in the beds of Lower Cretaceous age, but a transition into the 
Tertiary flora is evident in the latter almost from the start. Heer com- 
pares the Greenland beds of the Kome series with the Wealden series, 
the Atane series with the Cenomanian succession. The latter view has 
been favourably accepted, the former not; but, taking the Cretaceous 
flora in Greenland as a whole, Seward * regards it as representing more 
fully than elsewhere the transition between the Mesozoic and Tertiary 
floras. As a rule the comparison of late Cretaceous and Tertiary floras 
with living plants shows differences of geographical distribution and 
conditions, rather than essential differences in types. Dr. Stopes also 
has shown that the angiospermous woods from the Lower Greensand 
Series “ did not exhibit any primitive characters, nor any relationships 
with gymnospermous (cf. Bennettitales). They were ‘ like quite highly 
#2 Phil. Tvans. Roy, Soc., vol. B., p. 215 (1926). 
48 Phil. Trans. Roy. Soc., vol. B, p. 203 (1912). 
