1893. NOTES AND COMMENTS. 327 
whole of Europe and Asia. Hestates the following laws :—(1) When 
a chain of mountains, such as the Alps, the Pyrenees, separates two 
nations, . . . . one generally thinks that the crest, the water-shed, 
divides two races, each inhabiting his respective slope up to the 
summit. Nothing of the kind, and one can say that the crest of a 
chain does not separate two races. In support of this statement, 
Regnault says:—This error is due to the fact that the crest 
generally serves as a frontier between two States. (2) Ordinarily 
the race of the country towards which the lesser slope inclines 
inhabits not only this slope, but crosses the crest and colonises the 
more rapidly-sloping side down to the plain in which the slope is lost. 
It is the junction between the rapid slope and the plain where the 
contact of the tworaces is to be found. To the second law he adds 
two postulates:—(a) The mountain chain must be high and long, 
as the Alps and Pyrenees; (b)~The law is modified by considera- 
tions of time, geology, climate, &c. Dr. Regnault discusses in some 
detail the Alps, the Pyrenees, Erz-Gebirge, Caucasus, and the Hima- 
laya. The lecture, which is highly interesting, will be found 
printed in Revue de Géogvaphie, March, 1893. 

MYELOXYLON. 
In the recently-issued number of the Annals of Botany (vol. vil.,p.25), 
A. C. Seward discusses the affinity of the fossil plant genus Myeloxylon. 
Corda thought it a Palm, Brongniart a doubtful Monocotyledon, while 
Goeppert referred it to those plants which must be looked upon as 
prototypes or synthetic types, recognising in its structure the Fern, 
Gymnosperm and Monocotyledon. Binney, Williamson, Renault, 
and Kidston make it a fern rachis of the order Marattiacez, while 
Schimper, Schenk, and Felix prefer to regard it as the petiole of a 
Cycad. The present account embodies the result of an examination 
of some new material from the Millstone Grit, and elsewhere, and 
also of some specimens now in the British Museum, and once the 
property of Robert Brown. The’author has had the good fortune to 
get sections showing very well the structure of the vascular bundles, 
the form of which closely corresponds with that in Cycads of to-day, 
while the position of the first-formed wood vessels on the side of the 
wood next to the bast is also in striking agreement with these. The 
bordered pits, characteristic of the recent Cycads, were not seen, but 
there are points of resemblance between the wood elements in both, 
while the resin canals of recent Cycads and the fossil petioles are 
practically identical. 
On the whole, the author concludes that the fossil specimens 
approach more nearly tothe Cycads than the Ferns. The few points 
of difference which distinguish them from the petioles of recent 
Cycads are, he thinks, far outweighed by the close parallelism in 
more essential characters, and he looks upon Myeloxylon as an 
