in this way have been known for years to show no sign of microscopic life.
The question was regarded as settled, but in 1859 it was unexpectedly opened in Paris by Pouchet, who claimed that life was developed in organic fluids even after boiling and preventing the entrance of floating particles from the air. Pasteur, however, demonstrated that Pouchet had been careless, and had admitted solid particles to the flask in the mercury, through which the oxygen had been introduced into the flasks. This closed the question as far as it could be answered by experiment. Professor John Tyndall added something to the certainty of the matter by an ingenious experiment. He had an air-tight box made with glass-windows, through which he passed a strong beam of light in a darkened room. The floating particles in the air, contained within the box, fell of their own weight, and came to rest on the sides and bottom of the box, which had been smeared with a sticky substance to hold them. He could tell when the air was completely cleared of these particles by his beam of strong light, because any minute floating particle would become illuminated and reflect the light. When they had entirely come to rest, he called the air “optically pure.” Through the bottom of this box he had inserted a number of test-tubes with their mouths opening into the chamber, and, by means of a long funnel and a hole pricked in a rubber membrane at the top, he was able to introduce a variety of organic fluids into these test-tubes. The ends of the test-tubes outside of the box were now inserted into boiling oil and all germs of life that might be contained in the fluids were completely killed. He was able to expose the fluids in these open test-tubes to the optically pure air for months, without any appearance of microscopic life in any of them. To demonstrate that the fluids were capable of supporting such life, he had simply to open for a moment an air-tight door in the back of the chamber and admit some of the outside air. When this was done, the fluids became turbid in a short time, and were teeming with microscopic life. Thus it was demonstrated that microscopic life came from floating germs in the air, and is not spontaneously generated in organic fluids. See Tyndall in Pop. Sci. Mo. (vol. 12, 1878) and in Floating Matter of the Air.
Spoon′bill, the name of birds related to
the Ibises, having long, broadly expanded
bills, more like paddles than spoons. They
belong chiefly to the eastern hemisphere,
where there are six or seven species. The
European spoonbill is a white bird about 32
inches long. It breeds in Holland and other
parts of Europe. The roseate spoonbill is
the only American species. It is abundant
in the tropics and also breeds in the
southern
United States. These birds inhabit
marshes, muddy borders of estuaries and
WHITE SPOONBILL
small sea-islands
overgrown with
bushes. They are
from 28 to 35
inches in length,
of a beautiful
rose-color, deepest
on the wings,
fading to almost
white on the neck,
back and breast.
Their tail-coverts
are deep carmine.
They feed at night
by gathering
insects and
shellfishes from the mud in shallow water. In
the breeding season they congregate in
large numbers.
Sporangium (spō̇-răn′jĭ-ŭm), an organ of
plants which produces asexual spores. In
SPORANGIUM
OF A MOULD
the thallophytes a sporangium
is usually a single cell; but in
the higher plants it is a
many-celled organ. The sporangia
of ferns and the pollen-sacs of
seed-plants are illustrations of
many-celled sporangia. In
heterosporous plants sporangia
become differentiated, the
microsporangia producing
microspores, and the megasporangia
producing megaspores. In
seed-plants the pollen-sacs are
microsporangia, and the ovules
are megasporangia.
Spore, a plant-cell specially set apart for reproduction. Spores have received the greatest variety of names in different groups of plants, but they may all be reduced to two great groups. Asexual spores are those which are formed by the division of a cell, or at least are not formed by the union of cells; while sexual spores are those which are formed by the union of two sexual cells, called gametes. These two types of spores do not differ from one another in power, but in mode of origin. The sexual spore has received the general name of oöspore; but in plants in which the pairing gametes are similar it is more frequently called a zygospore or zygote. The asexual spores have received very many names. Among the green algae the characteristic asexual spore is a ciliated, free-swimming cell, and is called a zoöspore or swarm-spore. Among fungi, asexual spores have received such names as conidia, ascospores, uredospores, teleutospores, æcidiospores, basidiospores etc. Among bryophytes and pteridophytes they are known simply as spores. When heterospory is introduced, they become microspores and megaspores; and in spermatophytes they are known as pollen-grains and embryo-sacs. Such a
