The Philippine journal of science. [Vol. 57, no. 1]

THE PHILIPPINE
JOURNAL OF SCIENCE
VOL. 57 MAY, 1935 No. 1
GINKGO ADIANTOIDES (UNGER) HEER; CONTEMPORARY AND FOSSIL FORMS
By K. SHAPARENKO
Of the Botanical Institute, Academy of Sciences, Leningrad
ONE PLATE AND EIGHT TEXT FIGURES
While studying the paleobotanic specimens of the Leningrad
Section of the Research Oil Institute to identify the plant impressions collected by Geologist P. K. Ivanchuk in Miocene
deposits near the village Krymskaya in the northern Caucasus,
I found what I thought was a ginkgo. On further study I met
with various contradictory opinions, of diverse authors, as to
the specific Tertiary and Cretaceous peculiarities of this genus.
In past geologic epochs ginkgoes developed and spread rapidly
over the world. Their earliest representatives are found in the
Middle Devonian.' They attained their greatest development
during the Mesozoic era, especially in the Jurassic period. No
precise picture can be given of the evolution of the group in
different geologic periods. The leaves, upon which the classification of ginkgoes is based, have no connection with generative
organs and do not give us sufficient data. The Jurassic was the
culminating period of the ginkgoes. In Cretaceous deposits they
were mostly localized, filled small areas, and were less numerous
than in the preceding period.
Psygmophylltuin Kolderupii Nathorst, from the Middle and the Upper
Devonian in Norway, and P. Kiltorkense Johnson in Ireland [Krausel
(1926) and Zimmerman (1930)]. More recently some authors referred
these species to the ferns, which demonstrates the fundamental difficulties
of the systemization of ginkgoes in our study of these plants. In some
cases it is scarcely possible to distinguish the leaves of the ginkgo from
those of the fern.
2)1- f3 1