SECTIONAL TRANSACTIONS.—K. 491 
in the Cxsalpiniacee is described and is shown to constitute a dominant feature 
of the group. It is held that in the group petaloidy is an early declaration of 
advancing sterility, whose climax is total sterility and apetaly. The organisms 
considered are arranged in a series to illustrate the thesis that petaloidy is 
an index of recent sterilisation which marks a step in the decadence of an 
originally apetalous group. The persistent recurrence of petaloidy must lead 
to total sterility. It is held that if this interpretation of petaloidy in the 
Cesalpiniacee can be accepted broadly for Angiosperms, the latter must be 
viewed as decadent by a growing sterility of which petaloidy indicates an early 
stage. The need for systematic study of the physiology of these features is 
emphasised. 
24. Dr. E. N. Mires Tuomas.—Observations on the Seedling Anatomy 
of the Ebenales. 
Several new species and genera are described, including for the first time 
members of the family Stvracacez. 
Mr. H. Wright described the seedling anatomy of a number of species of 
Diospyros in 1904, and Miss W. Smith of the Sapotacee in 1908. They agree 
apparently in the prevalence of four root poles in the diagonal position, which 
is rare in other groups so far as is known. Hexarch forms, however, are also 
found and much variability exists, particularly in the Ebenacez. 
The present communication establishes the existence of ‘ cruciform ’ tetrarchy 
and diarchy (Diospyros Lotus, Styrax japonica, Halesia tetraptera), thus mini- 
mising the importance of the absence of root poles in the cotyledonary plane 
(Smith, ‘ Trans. Linn. Soc.,’ 1908). 
It further establishes the existence of ‘ alterne’ protoxylem, which is more 
or less resorbed at different levels (Diospyros, &c.). Thus the seedling anatomy 
of this very aberrant and variable Order is linked with the more usual types. 
25. Dr. W. R. G. Arxins.—Seasonal Changes in Water in Relation 
to the Algal Plankton. 
Sea water off Plymouth undergoes changes in hydrogen-ion concentration 
from pH 8.12 in winter to pH 8.24 in early summer as the algal plankton 
removes CO;; these progress from surface to bottom, uniformity being reached 
by October. 
The increase of plankton also results in a decrease of phosphate content 
from 0.05mgr, of P.O; per litre in winter to 0.004-0.002 for surface water in 
early summer, the diminution being observed at greater depths later. It appears 
probable that phosphate is the factor which limits algal multiplication, and 
consequently animal life also. 
In fresh water much larger variations in pH value are found. In shallow 
ponds phosphate may be used up completely in early summer, whereas in deep 
water relatively large amounts are still available. 
26. Prof. A. C. Sewarp, F.R.S.—Cretaceous Floras of Greenland. 
A preliminary account was given of the Cretaceous flora of Western Green- 
jand based on material collected by himself and Mr. R. E. Holttum in 1921. 
On the east side of Disko Island and on the coast of the Nugsuak Peninsula 
Cretaceous and Tertiary freshwater sedimentary rocks rest on the denuded 
surface of the Archean Gneiss and are covered by a succession of Tertiary 
basalts and volcanic ash. The vegetation present in the Cretaceous strata con- 
sists of ferns, especially species of Gleichenites, Conifers, Ginkgoites, and many 
Dicotyledons. It is clear that these plants must have lived under climatic con- 
ditions very different from those of the present day. A brief description was 
given of the more interesting genera and the question of the geological correla- 
tion of the Greenland beds with plant-bearing strata in other countries was 
discussed. 
