Page:Popular Science Monthly Volume 27.djvu/372

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THE POPULAR SCIENCE MONTHLY.

plant throughout life produces both forms, and on the same bough may be seen phyllodes interspersed among ordinary pinnate leaves, the respective advantages being, it would appear, so equally balanced that sometimes the one, sometimes the other, secures the predominance.

In the case of the eucalyptus, every one who has been in the south of Europe must have noticed that the young trees have a totally different aspect from that which they acquire when older. The leaves of the young trees (Fig. 18) are tongue-shaped, and horizontal. In older ones, on the contrary (Fig. 19), they hang more or less vertically, with one edge toward the tree, and are cimeter-shaped, with the convex edge outward, perhaps for the same reason as that suggested in the case of acacia. There are several other cases in which the same plant bears two kinds of leaves. Thus, in some species of juniper the leaves are long and pointed, in others rounded and scale-like. Juniperus chinensis has both.

In the common ivy the leaves on the creeping or climbing stems are more or less triangular, while those of the flowering stems are ovate-lanceolate, a difference the cause of which has not, I think, yet been satisfactorily explained, but into which I will not now enter.—Contemporary Review.

 

EARTHQUAKE PHENOMENA.
By RALPH S. TARR.

AT the present time the earth seems to be in a state of great seismological action. Different parts of the world have recently been disturbed by earthquakes which have caused wide-spread destruction. Those in Spain, which began December 24th, and have lasted, with slight interruption, down to the time of writing, have been among the most destructive of recent earthquakes. Over two thousand people have been killed, many more wounded, and thousands of houses destroyed. Such a state of affairs can not help arousing an interest in this phenomenon.

The earth is constantly quivering, some point on the surface being the seat of a slight quake nearly every moment of the day. By far the larger number of these are of little intensity, being felt only by delicate instruments, and the majority of cases come from volcanic regions. So few facts are known, that we can neither draw deductions nor even determine the causes. It is reported, however, that earth-quakes more commonly occur at night, and that they are more abundant in winter than in summer.

The only settled facts about earthquakes are, that they are the result of some shock imparted to the rocks at a considerable distance beneath the surface, and that this shock reaches the surface in a series