228 
NATURE 
3 [ Fan. 5, 1882 
requisite strength, rotate at a speed of 500 revolutions a 
minute. and in that time will do from 22 to 29 foot pounds 
of work. The construction is extremely simple. There 
is a Siemens’ armature on a horizontal axis, within, and 
entirely surrounded by, the fixed electromagnet which 
not only serves to produce a powerful magnetic field, but 
also acts as a rigid framework for the rotating parts, 
which is thus protected from injury. The contact of the 
wires of the circuit with the commutator is made by two 
springs with little metallic friction-rollers at the end. The 
ironwork is made of malleable cast-iron, and so combines 
the advantage of high magnetic power and of cheap pro- 
duction. Mr. Griscom, the inventor, styles his little 
machine the double-induction motor on account of the 
reaction between the currents in the armature and those 
which supply the outer field-magnets. The inventor 
originally intended his motor to be used with a 6-cell 
bichromate battery, and he claims that one single charge 
of acid liquid will last long enough to enable a sewing- 
machine fixed to a motor to accomplish from 500 to 1000 
yards of stitching. But there is no doubt that the motors 
work equally well with currents supplied from any other 
source in adequate strength. A gold medal was awarded 
at the late Paris Exhibition to Mr. Griscom for the 
excellence of his capital little machine. 
It will be remarked that in each of the little modern 
motors described a simple Siemens’ armature is employed 
in preference to one in the form of the Gramme ring or 
other complicated pattern. This is simply a consequence of 
the difficulty of constructing these more complex kinds of 
armature cheaply on a small scale. If they could be as 
cheaply constructed they would doubtless be preferable 
as having no dead points, and therefore not being liable 
to stick at starting, though this rarely happens with these 
little electric engines. It will also be noted that the last 
two forms are dynamo-electric instead of magneto- 
electric; that is to say their fixed magnets are electro- 
magnets of iron, not permanent magnets of steel. This 
is in order to gain space; for an electromagnet may be 
made far more powerful than a steel magnet of equal 
size, and therefore for an equal power the electromagnet 
will be of less bulk than the magnet of hard steel. 
A CHAPTER IN THE HISTORY OF CONIFER 
THE PODOCARPE 
ee tribe is limited to three genera. Nothing is 
known as to the ancestry of two of these—JZicr0- 
cachrys and Saxegothea, represented now by a single 
species each; but the third, Podocarfus, comprises fifty- 
nine species according to Gordon.! The fruits are 
drupaceous or nut-like, and the seed generally possesses 
a hard shell and contains a dicotyledonous embryo. The 
leaves are either distichous, like the yew, or imbricated, 
and vary from very small to several inches in length ; and 
although generally parallel-nerved, two species in the 
Kew Herbarium have distinctly dicotyledonous venation. 
Like the rest of the Coniferae, some species form colossal 
trees, exceeding 200 feet in height. They are classified in 
the “Genera Plantarum” into four groups—JVageva, which 
contains the only Conifer indigenous to the East Indies; 
Eupodocarpus, comprising the vast majority of the species; 
Stachycarpus, and Dacrycarpus. The two latter sections 
are represented in the Eocene, and are at present limited 
to the Malay Archipelago, Australia, New Zealand, and 
South America. Notwithstanding their immense distribu- 
tion and the evidence of vast antiquity which the genus 
presents, scarcely anything is known of their past history. 
In most cases the foliage when detached has little to dis- 
tinguish it from better-known Conifer, and the fruits, in 
the fossil condition, seldom present anything by which 
their gymnospermous origin can be inferred. Except a 
* Sir Joseph Hooker believes they may eventually be reduced to less than 
orty, since several are very imperfectly known. 
doubtful and undescribed species from Aix-la-Chapelle, 
no podocarp is known of earlier age than Eocene, and 
they disappear from temperate Europe with the Oligocene. 
Like the Araucaria and other genera innumerable, they 
seem to oppose the theory that all plants have originated 
in northern regions, and passed south by way of existing 
continents ; and unless it is supposed that their present 
distribution was accomplished prior to the Cretaceous, we 
are forced to admit, in order to explain their presence in 
Chili and other parts of South America, a land connection 
far to the south of that admitted by Wallace and those 
who share his opinions. No trace of podocarp has in 
fact been made known either from the Arctic or the 
American Cretaceous and Tertiary floras. 
The fossil Podocarps that are known may be con- 
veniently classified under two heads—those that have 
shed their leaves separately, and those that have shed 
them adhering to branchlets. 
Of the former, various species have been described by 
Saporta, Heer, Unger, Ettingshausen, and others, ranging 
in time from the Suessonian to the lowest stage of the 
Aquitanian. They therefore form a group in Central Europe 
essentially characteristic of the Eocene, and are quite un- 
known in the Miocene, except in Italy. They occur at Aix, 
Lat. 43°, and extend upto about Lat. 48°, which represents 
their Eocene distribution as at present published. It may 
therefore emphasise the importance attaching to a proper 
examination of our British Eocene floras, when I state that 
they have now been found not only at Bournemouth, but 
in Antrim and in Mull, or as far north as about 564°. The 
British species differs from all those previously figured, 
forithas a broadly sessile and articulated base, whilst 
the others are represented as tapering to a fine point. 
The leaves, though scarcely 2 mm. broad, sometimes 
reach 5 inches in length. Those from Mull, and, as 
far as can be seen, the half-leaf from Antrim, are specifi- 
cally identical with the Bournemouth form, and this is 
the more remarkable since the latter is confined to the 
uppermost bed under the Coastguard Station, and has 
never been found in any of the other numerous beds 
from which I have so largely collected. Of the Conti- 
nental species, the nearest to it are mostly from Aix, 
whose flora in several other respects presents the greatest 
affinities with ours. Besides the identity in appearance 
of some of the leaves with many existing Podocarps, 
as P. andina, the microscopic structure of the leaves and 
wood peculiar to them was recognised and explained by 
Unger. I have not seen any records of the fruits being 
found, and although some from Bournemouth might 
belong to the species, no essential character is preserved. 
Of the Podocarps whose leaves are shed attached to 
branchlets, only the most insignificant traces have been 
hitherto known. I have now to add at least two species 
whose foliage, fruit, and flowers are preserved. 
The first and most ancient is from Alum Bay, and has 
hitherto been supposed a Sequoia, a Taxus, a Cypress, 
&c., by distinguished Continental professors who have 
examined it. Possessing polymorphic foliage, it falls into 
the ‘‘Dacrycarpus’’ division of Hooker. By far the 
larger proportion of the foliage collected is distichous, 
being much smaller than that of the yew, with the bases 
of the leaves prolonged down and adhering to the 
stem, and with three out of the five rows, though still 
recognisable, reduced to small dimensions. This abor- 
tion of some of the leaves, in order to permit the remain- 
der to expand into two lateral rows, is exceedingly charac- 
teristic of ancient Conifer, and still survives in Sequoia, 
being probably the precursor of the truly distichous 
arrangement seen in Taxus, Taxodium, Toveya, and 
other existing Conifers. The fruit is small, petiolated, 
and remarkable as occurring on the distichous branches. 
The fossils of Alum Bay were, unfortunately, collected 
principally for sale, and the unattractive imbricated 
branchlets and the insignificant-looking fruit were doubt- 
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