VEGETATION
Since closer acquaintance takes from the _maria_ their character of
seas, we are led to inquire again into their constitution. Now, when we
set ourselves to consider to what such appearances could be due we note
something besides sea, which forms a large part of our earth’s surface,
and would have very much what we suppose the latter’s aspect from afar
to be, not only in tone, but in tint. This something is vegetation.
Seen from a height and mellowed by atmospheric distance, great forests
lose their green to become themselves ultramarine.
To dispossess a previous conception is difficult, but so soon as we
have put the idea of seas out of our heads a vegetal explanation proves
to satisfy the phenomena, even at first glance, better than water
surfaces. In their color, blue-green, the dark areas exactly typify the
distant look of our own forests; whereas we are not at all sure that
seas would. From color alone we are more justified in deeming them
vegetal than marine. But the moment we go farther into the matter the
more certain we become of being upon the right road. With increased
detection the markings they reveal and the metamorphoses they undergo,
while pointing away from water, point as directly to vegetation. All
the inexplicabilities which the supposition of water involves find
instant solution on the theory of vegetal growth. The non-balancing of
the areas of shading in their shift from one part of the disk to
another, no longer becomes a circumstance impossible to explain, but a
necessary consequence of their new-found character, denoting the time
necessary for vegetation to sprout. The change of hue of vast areas
from blue-green to ochre no longer presupposes the bodily transference
of thousands of tons of substance, but the quiet turning of the leaf
under autumnal frosts. Even the fact that they occupy those regions
most fitted by figure to contain oceans fits in with the same
conception. For that the Martian equivalents of forest and moorland,
tree and grass, should grow now in the lowest parts of the planet’s
surface is what might not unreasonably be expected from the very fact
of their being low, since what remained of the water would tend both on
the surface and in the air to drain into them.
[Illustration: Mare Erythræum
Martian date. December 30]
For the change in question to be vegetal it must occur at the proper
season of the planet’s year. This we must now consider. We have said
that Schiaparelli detected change in the blue-green regions and
suspected this change of seasonal affiliation. He inferred this from
piecing together the aspects of different seasons of different years as
shown in consecutive Martian oppositions. To mark it actually take
place in a single Martian year came later. In 1894, at Flagstaff, the
southern hemisphere was presented during its late spring and early
summer; it was observed, too, for many of our months in succession.
During this time the planet was specially well circumstanced for study
of the change in that hemisphere, both by reason of the appositeness of
the season and of the unusual size of the disk. Advantage was taken of
the double event to a recording of the consecutive appearances certain
regions underwent, and the contrasted states thus exhibited were such
as clearly to betoken the action of seasonal change. What Schiaparelli
had thus ably inferred from diverse portions of different Martian years
was in this case shown occurring in one and the same semestral cycle.
Usually the change of hue seems essentially one of tone; the blue-green
fades out, getting less and less pronounced, until in extreme cases
only ochre is left behind. It acts as if the darker color were
superimposed upon the lighter and could be to a greater or less extent
removed. This is what Schiaparelli noted and what was seen in 1894 at
Flagstaff. Three views _en suite_ of the chain of changes then observed
are shown in _Mars_, the region known as Hesperia being central in
each. Comparison of the three discloses a remarkable metamorphosis in
that “promontory,” a rise into visibility by a paling of its
complexion. Nor is the contrast confined to it; changes as salient will
be noticed in the pictures over the other parts of the disk.
There have been instances, however, of a metamorphosis so much more
strange as to deserve exposition in detail; one where not tone simply
is involved, but where a quite new tint has surprisingly appeared.
[Illustration: Mare Erythræum
Martian date. January 16]
On April 19, 1903, when, after being hidden for thirty days, owing to
the different rotation periods of the two planets, the Mare Erythraeum,
the largest blue-green region of the disk and lying in the southern
hemisphere, rounded again into view, a startling transformation stood
revealed in it. Instead of showing blue-green as usual, and as it had
done six weeks before, it was now of a distinct chocolate-brown. It had
been well seen at its previous presentation, so that no doubt existed
of its then tint. At that time the Martian season corresponded to
December 30 in our calendar. Eighteen Martian days had since elapsed,
and it was now January 16 there. The metamorphosis had taken place,
therefore, shortly after the winter solstice of that part of the
planet. The color change that had supervened proved permanent. For the
next night the region showed the same brown hue, and so it continued to
appear throughout the days that it was visible. Two months passed, and
then the chocolate hue had vanished,—gone as it had come,—and the
_mare_ had resumed its usual tint, except for being somewhat pale at
the south. It had come to be February 21 on Mars. Timed and tabulated,
the metamorphosis through which the _mare_ passed stands out thus:—
MARE ERYTHRAEUM 1903
============+================+=============+==================
| DAYS BEFORE OR | |
| AFTER SUMMER | |
MUNDANE | SOLSTICE | MARTIAN |
DATE | (BEFORE = - | DATE | ASPECT
| AFTER = +) | |
------------+----------------+-------------+------------------
February 16 | -10 | December 16 | Blue-green
March 20 | +22 | January 1 | Blue-green
April 19 | 52 | January 16 | Chocolate
April 22 | 55 | January 18 | Chocolate
May 26 | 89 | February 4 | Faint chocolate
May 30 | 93 | February 6 | Faint chocolate
June 30 | 123 | February 22 | Faint blue-green
July 7 | 130 | February 25 | Faint blue-green
============+================+=============+==================
The culmination of the transformation seems to have taken place about
60 days after the southern winter solstice, or in the depth of the
Martian winter of that hemisphere. This is certainly just the time at
which vegetation should be at its deadest.
The northern and southern portions of the _mare_ did not behave alike
in taking on the chocolate tint. From the notes made about them during
the opposition it appears that the latter was later than the former in
undergoing the metamorphosis, as will be seen from the following depth
of the blue green estimated in percentages shown at different dates,
calling the deepest tone ever exhibited by it unity.
=========+==========+=========+=========+==========+==========
MARTIAN | DECEMBER | JANUARY | JANUARY | FEBRUARY | FEBRUARY
DATE, | (16) | (1) | (17) | (5) | (24)
---------+----------+---------+---------+----------+----------
| % | % | % | % | %
Northern | 50 | 50 | 0 | 25 | 50
Southern | 50 | 50 | 0 | 0 | 25
=========+==========+=========+=========+==========+==========
From this table we may place the lowest point of the blue-green tint as
reached about the 22d of January for the northern, the 5th of February
for the southern, part. This would indicate that the wave of returning
growth came from the north, not the south; an important fact, as we
shall see later in studying the action of the canals.
[Illustration: Mare Erythræum
Martian date. February 1]
At the next opposition, in 1905, a recurrence of the transformation was
watched for, and not in vain. It occurred, however, somewhat later in
the Martian season. On December 27 of the planet’s current year the
Mare Erythraeum was still as usual, blue-green, nothing out of the
ordinary being remarked in it; and so it was on its January 17,
although the southern edge was darker than the northern. It looked
certainly as if the metamorphosis were this year to be omitted. But
such was not the case. When the region again came round, on February 1
of the Martian calendar, there the strange tint was as unmistakable as
it had been on its original occurrence. Not only was the Mare
Erythraeum so colored, but on February 5 (Martian) the northern portion
of the Mare Cimmerium was observed to be similarly affected. In the
Mare Erythraeum the anomalous chocolate hue was confined to a belt
between the latitudes of 10° and 20° south of the equator; in the Mare
Cimmerium it stretched a little higher, from 10° at the west to 25° at
the east. It is noteworthy that the southern portion of the latter
showed blue at the time the northern showed brown. Then the
metamorphosis proceeded as shown in the following table:—
MARE ERYTHRAEUM 1905
===========+======================+=============+=================
| DAYS AFTER WINTER | |
MUNDANE | SOLSTICE OF SOUTHERN | MARTIAN | ASPECT
DATE | HEMISPHERE | DATE |
-----------+----------------------+-------------+-----------------
January 25 | 12 | December 27 | Blue-green
March 6 | 52 | January 16 | Blue-green
April 4 | 81 | January 31 | Chocolate
April 12 | 89 | February 4 | Chocolate
April 30 | 107 | February 13 | Faint chocolate
May 8 | 115 | February 17 | Faint chocolate
May 12 | 119 | February 19 | Faint blue-green
June 11 | 149 | March 6 | Faint blue-green
June 15 | 153 | March 8 | Faint blue-green
July 16 | 184 | March 23 | Pale bluish green
===========+======================+=============+==================
Here, as in 1903, a chromatic rise and fall is evident; the culmination
of the change occurring in Martian early February about ninety days
after the winter solstice. That it was not of long duration is also
indicated. If we examine the evidence for the two portions of the
_mare_ separately, the northern and the southern, as in 1903, we find
it as follows:—
=========+==========+=========+==========+==========+=======+========
| | | | | |
MARTIAN | DECEMBER | JANUARY | FEBRUARY | FEBRUARY | MARCH | MARCH
DATE, | (27) | (16) | (2) | (16) | (7) | (23)
---------+----------+---------+----------+----------+-------+--------
| % | % | % | % | % | %
Northern | 50 | 50 | 0 | 10 | 25 | 30
Southern | 50 | 50 | 20 | 20 | 25 | 30
=====================================================================
Here again a slight retardation in the advent of the metamorphosis is
observable in the southern portion.
There would seem to be a difference in the time of the change between
the two years of fifteen days, 1905 being by that much the later. But
with points of reference themselves thirty days apart, it is possible
the two more nearly coincided than here appears.
Unlike the ochre of the light regions generally, which suggest desert
pure and simple, the chocolate-brown precisely mimicked the complexion
of fallow ground. When we consider the vegetal-like blue-green that it
replaced, and remember further the time of year at which it occurred
upon both these Martian years, we can hardly resist the conclusion that
it was something very like fallow field that was there uncovered to our
view.
[Illustration: Mare Erythræum
Martian date. February 21]
From the recurrence of the phenomenon on two successive years, it is
likely that it annually takes place. That it is seasonal can scarcely
be doubted from the timeliness of its occurrence, and that different
portions of its terrane successively underwent their metamorphosis
shows further that it followed a law peculiar to the planet, to which
we shall be introduced when we come to consider the phenomena of the
canals.
Instances of relative hue in different dark patches corroboratory of
seasonal variation, and therefore of vegetal constitution, might easily
be adduced. Thus, in 1905 during the summer of the northern hemisphere,
the Mare Acidalium was notably darker than the Mare Erythraeum to the
north of it, which is what the law of seasonal variation would require,
since it was June in the one, December in the other at the time. But we
need not to add example to example or proof to proof, for there are no
phenomena that contradict it. We conclude, therefore, that the
blue-green areas of Mars are not seas, but areas of vegetation. Just as
reasoning to a negative result drifts us to the first conclusion, so
reasoning to a positive one lands us at the second.