visit, we had time for only one--a horseback ride to the Howgelgait
Cañon. The ride was most enjoyable in every respect. The road leads
from the town up over the plateau through the burying ground, and
then on through a partly cleared forest of cottonwoods and maples.
Then we plunge into a two-mile-long lane, the trail scarcely wide
enough to admit of the passing of a horse, through a dense grove of
hazel bushes, laden to their tips with unripe nuts still protected
by their green fuzzy envelopes; and now we knew whence came the name
"Hazelton." Suddenly the grove terminates, and after dismounting and
walking forward a few steps we came to the face of the cañon. What
a sight! On the opposite cliff, but on a higher level, stands the
old deserted village of Howgelgait, with its great empty houses and
skeleton totem poles. At our feet, down a sheer precipice almost a
thousand feet below, the Bulkley River, set on edge, rushes and roars
and foams through the rocky gorge to join the Skeena a mile away.
Just by the mouth of the cañon, at the edge of the great whirlpool,
and on a gravelly beach, stands the present town of Howgelgait.
Hearing shouts, we looked closer, and far down we saw men moving
about, their forms dwarfed to almost spiderlike dimensions. They were
building a swinging bridge over the river, and the timbers already in
place looked like the meshes of a spider's web.
Looking up the cañon, we could see from the opposite wall near the
water's edge, and far below us, a rude scaffolding suspended by bark
ropes over the river, and from this Indians were lowering their
nets and drawing up salmon. One man after another would leave for
his home, his back bending under the weight of many fish, his place
to be taken by another, who begins casting his nets. And so these
rude scaffoldings here and all along the rivers are occupied by busy
fishermen throughout the summer, for salmon is chief of the winter's
food supply of these people. In one house we saw over a thousand
salmon hung up to dry for use during the winter months.
We left the cañon for the ride back to Hazelton with keen regret, for
no more fascinating spot did we find on our entire journey than right
here. On the way we encountered a woman of the Carrier tribe of the
Tinnehs from Frazer's Lake, who was returning from Hazelton laden
with provisions and cheap calicoes.
We had scarcely entered Hazelton when the tinkling of the bell of the
"lead horse" announced the arrival of the pack train. Second only in
importance to the arrival of the Caledonia to the people of Hazelton
is the arrival of the pack train, for it brings the news of the far
interior. But of much greater importance and value is the cargo of
furs which are brought out on every trip in exchange for supplies
which are taken in. On that day there were fifty-seven mules, each
laden with two bales of furs weighing two hundred and fifty pounds,
and including beaver, mink, otter, sable, and bear, all destined for
the Hudson Bay Company's house in London, there to be auctioned off
in lots to the highest bidder, and then to be distributed to all
parts of the civilized world.
[Illustration: HAGIVILGAIT CAÑON, WITH INDIAN FISH WEIRS AT BOTTOM.]
Within less than an hour's time the precious furs were aboard, and we
bade farewell to Hazelton. The Caledonia drops back, is slowly turned
around by the current, and with its steady chug, chug, we began our
journey down the river, the power of the boat aided by the swiftly
flowing water carrying us along at a rapid rate. If the slow, labored
up journey was a revelation with its worries and anxieties, what can
be said of the down journey with its kaleidoscopic panorama of sand
bars, Indian villages, far-away snowy mountains, dense forests of
mighty cottonwoods, lofty heights which tower above us clad to their
very summits with eternal green, mountain streams, and innumerable
waterfalls and cascades! And what shall one say of that memorable
ride through the cañon, the wheel reversed and throwing water over
the pilot house, the boat rocking and swaying to and fro! Before we
were fairly aware of the fact we were out into that great, deep,
silent basin again and off on the home stretch. Apart from taking on
wood and stopping at one or two Indian villages, a delay of a few
hours was made to permit some mining engineers to examine a mine.
They had just come up from the coast and brought with them news of
the gold excitement in the Yukon Valley, and now for the first time
we heard that magic word "Klondike," which was soon to "electrify
the world and put the gold fields of California, South Africa, and
Australia to shame."
At nine o'clock we were in Essington once more. "Klondike, Klondike!"
on every side. The whole country seemed to have gone daft. One
steamer after another went racing by the mouth of the Skeena on the
way to Dyea and the Skagway Trail. But our fortunes lay in the other
direction, and that night we were aboard the Islander, bound for
Victoria and the south.
FOOTNOTE:
[25] From a lecture delivered at the Field Columbian Museum, November
13, 1897.
LIGHT AND VEGETATION.
BY D. T. MACDOUGAL, PH. D.,
PROFESSOR IN CHARGE OF PLANT PHYSIOLOGY, UNIVERSITY OF MINNESOTA.
Light is the most important of all the external agencies which
influence the vegetal organism, and the sun's rays have been the most
potent force in shaping the development of existent plant forms.
The sunbeam stands in a manifold relation to the plant. First and
foremost, light is the universal source of energy, by the aid of
which the chlorophyll apparatus in green leaves builds up complex
food substances from simple compounds obtained from the soil and air,
a process necessary for the nutrition of the entire living world.
Some obscure organisms, such as the "nitrosomonas," soil bacteria,
are able to accomplish the construction of complex substances, by
means of energy derived from other chemical compounds, which were,
however, formed originally by green plants. These food-building
processes are designated as photosynthesis, chemosynthesis,
electrosynthesis, thermosynthesis, etc., according to the source of
energy used.
By photosynthesis, carbon dioxide from the air and water from the
cell are combined in the green cells of leaves, forming sugar and
possibly other substances. During this process an amount of oxygen
approximately equal to that of the carbon dioxide taken up is
exhaled. It will be of interest to note the relation of the living
world to the atmosphere. Eight hundred to nine hundred grammes of
carbon dioxide are produced in the respiration of a single person
for a day, and the entire product of the human race for this period
is twelve hundred million kilogrammes. In addition, large quantities
of the gas result from the combustion of the four hundred and sixty
millions of kilogrammes of coal and wood burned yearly. The lower
animals, fungi, and green plants themselves contribute an amount
which must bring the total to twice the immense sum named above.
The atmosphere contains three or four hundredths of one per cent of
carbon dioxide, or an amount of about two to three thousand billions
of kilogrammes. No especial variation in this proportion has been
detected since observations upon this point were first made. The
fact that no increase takes place is partly due to the absorption
of the gas by plants, and its replacement by oxygen, and also to
certain geological processes in constant operation. Absorption
takes place at the rate of about two and a half grammes for every
square metre of leaf surface per hour, or about twenty-five to
thirty grammes daily, since the process goes on only in daylight.
It is to be seen that a single human being exhales as much carbon
dioxide as may be removed from the air by thirty or forty square
metres of leaf surface. According to Ebermayer, a hectare (2.47
acres) of forest would use eleven thousand kilogrammes of carbon
dioxide yearly, and the amount used by plants is generally much in
excess of that furnished by the activity of the inhabitants of any
given area. Plants thrive and show increasing vigor as the amount of
carbon dioxide in the air rises until two hundred times the present
proportion is reached. An increase of the gas in the atmosphere would
therefore be partly corrected by the absorption and by the stronger
vegetation induced. Nothing short of a comprehensive cataclysm could
work such disturbance to the composition of the air as to endanger
the well-being of the animal inhabitants of the earth.
The activity of a square metre of leaf surface results in the
formation of one and a half to two grammes of solid substance
per hour in sunlight. A vigorous sunflower with one hundred and
forty-five leaves constructed thirty-six grammes of solid matter in
a day, and a squash with one hundred and sixteen leaves one hundred
and sixteen grammes in the same length of time. The amounts formed by
such trees as the beech, maple, oak, poplar, elm, and horse-chestnut,
with leaf surfaces aggregating three hundred to one thousand square
metres, must be correspondingly large.
A comparison of plants grown in strong sunlight, diffuse light,
and darkness will reveal many differences in stature and internal
structure. These differences are for the most part due to the
_formative_ and _tonic_ effect of light. Otherwise expressed,
the influence of variations of light upon plants causes adaptive
reactions, and disturbances of the nutritive processes and growth.
In consequence of these facts the reaction of any given organ to
changes in the intensity of the illumination will depend upon its
specific functions and relation to the remainder of the organism.
The stems formed by seedlings and awakening underground organs are
usually surrounded by plants or other objects which cut off more or
less sunlight. The developing shoot can not spread its leaves to the
light advantageously until it has outstripped or grown beyond the
objects intervening between it and the light. This necessity is one
of the most important conditions in the struggle for existence. To
meet it, a very great majority of seed-forming plants have acquired
the power of accelerated elongation of the stems when deprived of
their normal amount of light.
Very striking examples of this reaction are offered by the awakening
corms of the Jack-in-the-pulpit (_Arisæma triphyllum_). The corms
usually lie at a distance of five or six centimetres below the
surface of the soil, and when the growth of the large bud begins
in the spring the heavy sheathing scales elongate and pierce the
soil, opening when the surface is reached at the distance of a few
centimetres. If the corm should have been buried deeper in the
substratum by floods or drifts of leaves, the growth of the bud
scales will continue until the light is reached, though it may be a
distance of twenty centimetres. Such growth may be seen if the corms
are grown in a deep layer of sphagnum moss, or in a dark room.
After the stems emerge from the "drawn" buds they show a similar
attenuation, attaining a length of twice the normal. The excessive
elongation of stems is accompanied by variations in the structure and
contents of the tissues. The cells are generally longer, while the
walls are thinner. In consequence, organs grown in darkness are very
weak and easily bent or broken. Growth in darkness is attended by the
non-formation of chlorophyll. This is replaced by etiolin, giving the
plant a pale, waxy, yellow appearance.
The adaptive elongation is not shown by all species, however. It
has been found that stems of beet, hop, dioscorea, and a few others
show no adaptations to diminished light. The adaptive modification
of stems elongating in darkness is developed from the retarding
influence exercised by light upon growth. Thus it is a well-known
fact that the action of certain portions of the sun's rays actually
impedes or checks the increase in volume known as growth, though it
does not influence actual division of the cells to any great extent.
When this retarding action is eliminated excessive elongation ensues.
The behavior of leaves in illuminations below the normal depends upon
the relation of these organs to the storage structures of the plant
as well as upon other factors, and many types are dependent upon
their own activity for plastic material necessary for growth.
It is to be said in general that leaves of dicotyledonous plants are
incapable of full development in darkness, though to this rule there
are many exceptions. Thus the leaves of the beet develop normally, or
nearly so, in darkness.
On the other hand, leaves of monocotyledonous plants attain normal
size in darkness, especially those with straight or curved parallel
venation. Some, as the iris, swamp marigold, and onion, attain a
greater length in darkness than in light. Here, as in stems, cell
division is not modified, but the growth of the individual cell is
increased.
The growth of leaves in darkness may be easily observed if the
underground perennial stems of common mandrake are placed in a dark
chamber before the growth of the leaf buds has begun. The leaves
are peltate, and in the bud are folded about the end of the petiole
after the manner of an umbrella. Usually this umbrella expands as
soon as it has pushed upward and become free from the soil, attaining
a diameter of twenty-five to forty centimetres when outspread. In
darkness, however, it refuses to unfold, the laminæ are pale yellow
and retain the crumpled form of the bud, and as the petiole shows
an exaggerated elongation the organ takes on the appearance of a
very small parasol on a very long handle. The imperfect development
of leaves and the rapid decay of aërial organs deprived of sunlight
leads to the conclusion that the action of light is necessary to the
health and normal activity of these organs, and the light therefore
exercises a _tonic_ influence upon vegetation.
Many species of plants are so plastic and capable of such ready
response to variations in external conditions that they undergo
distinct morphological changes in response to variations in the
intensity of the light. The common potato is an example of this
fact. The edible tubers are simply thickened stems, and the plant
has the habit of storing starch in any stems not acted upon by
the light. The branches arising from the base of the main stem
are generally underneath the surface of the soil, and afford the
proper conditions for tuber formation. Sugar is constructed in the
leaves, carried down the length of the stem, and deposited in the
underground branches as starch. Space is made for the accumulating
store by the multiplication of the thin-walled cells of the pith. If
any of the upper branches should become shaded, they become at once
the focus of converging streams of sugar, and similar enlargement
ensues, resulting in the formation of tubers. Such structures are
occasionally observed in plants grown thickly together.
Vöchting, by a number of most ingenious experiments, has succeeded in
producing tubers on any branch of a potato plant by simply inclosing
the branch in a small dark chamber. As the result of one experiment
the entire main stem springing from a sprouting tuber was converted
into a new tuber nearly as large as the first. The entire plant at
the close of the experiment had the form of a dumb-bell, with the old
tuber as one ball and the new tuber as the other.
The same writer has described important results obtained from a study
of the action of light upon the stems of cactus, consisting of a
number of flattened internodes. When the growing tips of such plants
were allowed to develop in a dark chamber the new internodes grown
were cylindrical in form. Such behavior suggests that these plants
were originally furnished with cylindrical stems and foliar leaves.
The leaves at some time in the history of the plant were found
unsuitable, and gradually atrophied, while the stems were flattened
and extended to take up their functions.
Some very striking adaptations of form of organs to the intensity
of the light have been analyzed by Goebel. The common harebell
(_Campanula rotundifolia_) has an upright stem twenty to sixty
centimetres in height. The upper part of the stem bears sessile
lanceolate leaves, decreasing in size from the base to the summit.
The first leaves formed by the stem on its emergence from the soil
are entirely different in construction, showing a heart-shaped lamina
with a distinct petiole. These leaves are formed at the actual
surface of the soil, are generally more or less shaded or covered by
fallen leaves, and in fact are not known or seen by many collectors
or observers of the plant. Goebel found that similar leaves might be
formed on any part of the plant if it were shaded from the full glare
of the sun's rays. The cordate leaves at the base of the stem were
always produced, however, no matter to what intensity of illumination
that part of the plant was subjected. It is therefore safe to
conclude that the cordate leaves are inherited forms, and that the
lanceolate organs are adaptations to light which may be shown by any
individual of the species.
In general it is to be said that the leaves of sun-loving species
have a thick epidermis, entirely free from chlorophyll, with stomata
on the lower side only, a firm consistence due to the formation of
woody tissues, and are often provided with a coating of hairs. The
leaves of shade-loving plants, on the other hand, have a thin-walled
epidermis often containing chlorophyll, stomata on both sides, and
are not so plentifully provided with hairs as those in exposed
situations.
The variations in external form described above are due to the
intensity of the illumination. At the same time the structure and
arrangement of the cells depend on the direction from which the
light rays come. Thus, an organ receiving light from one side only
will exhibit a structure different from an organ of the same kind
receiving direct rays from two or more sides. Light, then, is a
cause of dorsiventrality--that is, of the fact that the upper and
lower sides of organs are not alike in structure. The leaf affords a
splendid example of dorsiventrality as a result of the exposure of
one side only to direct light. The upper side of a horizontal leaf,
such as the oak, beech, or maple, contains one or two layers of
cylindrical cells with their long axes perpendicular to the surface.
In vertical leaves, such as the iris, these _palisade_ cells, as
they are termed, are not so well defined, and in all leaves grown in
darkness this tissue is very much reduced. If a young leaf not yet
unfolded from the bud is fastened in such a position that the under
side is uppermost, palisade cells will be formed on the side exposed
to the direct rays of the sun.
The influence of light upon the sporophylls, or reproductive organs
of the seed-forming plants, is quite as well defined as upon the
vegetative organs.
In general it is to be said that stamens and pistils may reach
functional maturity in darkness or diffuse light, and if pollination
is provided for, seed and fruit formation may ensue.
The diminution of light has the effect of transforming inflorescences
into leafy shoots in some instances, however. The more common
reaction consists of alterations in the size, form, and color
of the perianth, and greater changes are induced in the petals
than in the sepals. The corolla shows greater decrease in size in
_Melandryum_ and _Silene_, in diffuse light, though the relative
form is maintained. The writer has obtained most striking results
from growing flowers of _Salvia_ (sage) in a dark chamber, inclosing
the inflorescence only. In the normal flower the irregular scarlet
corolla attains three times the length of the calyx, and two stamens
extrude from under the upper lip. When grown in darkness, the corolla
with the adherent stamens measure about three millimetres in length,
or one twelfth the normal, and are scarcely more than half the size
of the calyx, which is but two thirds the size of similar organs
grown in the light. The color is entirely lacking from the corolla,
and is found only along the veins of the calyx.
In other instances in which the corolla is composed of separate
members, an unequal reaction is exhibited. The corolla of nasturtium
(_Tropæolum majus_) consists of five approximately equal petals.
Flowers of this species grown in darkness show one of nearly normal
stature, two of reduced size, while the remaining two take the form
of club-shaped bracts.
The diminished size of the perianth of cleistogamous flowers of such
types as the violet is due directly to the action of diminished light
upon the hidden or inclosed flower.
The influence of light upon the structure, reproductive processes,
and distribution of the lower forms brings about the most widely
divergent reactions, which can not be described here.
The distribution and color of marine algæ depend upon the depth of
the water and the consequent intensity of the light. This gives
rise to distinct zones of aquatic vegetation. Thus in one series of
surveys the _littoral_ zone, the beach area covered at high water
and exposed at low water, was found to furnish proper conditions
for green, brown, and red algæ. The _sublittoral_ zone, extending
to a depth of forty metres, is furnished with red algæ, increasing
in number with the depth, and the brown algæ disappear; while
the _elittoral_ zone, from forty to one hundred and ten metres,
is inhabited by red algæ alone. The number of species of vegetal
organisms below this depth is extremely small. An alga (_Halosphæria
viridis_) has been brought up from depths of one thousand to two
thousand metres.
A very great number of bacteria are unfavorably affected by light,
and find proper conditions at some depth in the soil or water. It
is on account of this fact that the water of frozen streams becomes
more thickly inhabited by certain organisms than in the summer
time, and exposure to sunlight is adopted as a hygienic measure in
freeing clothing and household effects from infection. Bacteria occur
abundantly in sea water at depths of two hundred to four hundred
metres, and quite a number of species are to be found at eight
hundred to eleven hundred metres.
The distribution of fungi follows the general habit of bacteria in
that they thrive best in darkness.
It is to be noticed in this connection that light is also a
determining factor in the distribution of the higher land plants.
Thus the amount of light received in polar latitudes is quite
insufficient for the needs of many species, entirely irrespective of
temperature.
The retarding influence of light upon growth is even more marked in
the lower forms than in the higher. Such action is the result of
the disintegrating effect of the blue-violet rays upon ferments and
nitrogenous plastic substances.
The greater massiveness of the bodies of the higher plants enables
them to carry on the chemical activities in which these substances
are concerned in the interior, where the intense rays may not
penetrate. The attenuated and undifferentiated fungi must seek the
shade, to escape the dangers of strong light, against which they have
no shield.
The reproductive processes are particularly sensitive to
illumination. The formation of zoöspores by green felt (_Vaucheria_)
may occur only in darkness, at night, or in diffuse light, and these
examples might be multiplied indefinitely. Many features of the
germination of spores and the growth of _protonemæ_ or _prothallia_
among the mosses, liverworts, and ferns are determined by light.
Perhaps the most striking reactions of plants to light are to be seen
in locomotor and orientation movements.
Locomotor movements are chiefly confined to lower forms, and are most
noticeable in the "swarm spores," or zoöspores of the algæ, though
exhibited by spermatozoöids as well. Zoöspores may be seen collected
against the side of the vessel receiving direct sunlight, while the
opposite side of the vessel will be free from them. The chlorophyll
bodies of green cells arrange themselves similarly. The latter bodies
may move away from the exposed side of the cell if the light exceeds
a certain intensity.
The typical plant may not move its body toward or away from the
source of light, but it may secure the same end by dispositions of
its surfaces to vary the angle at which the rays are received. This
form of irritability is one of the most highly developed properties
of the plant. Wiesner has found that a seedling of the vetch is
sensitive to an amount of light represented by one ten-millionth of
a unit represented by a Roscoe-Bunsen flame. The "sensitiveness"
to light may take one of three forms: The organ may place its axis
parallel and pointing toward the source of the rays, as in stems,
when it is said to be _proheliotropic_; the axis of the organ may
assume a position perpendicular to the rays, which is designated as
_diaheliotropism_; or it may place its axis parallel to the rays and
pointing away from the light, when it is said to be _apheliotropic_.
Upright stems are proheliotropic, horizontal leaves and creeping
stems are diaheliotropic, and roots and such stems as those of ivy
are apheliotropic.