expansion of the body-covering would be by an imbibition of water from the outside, and a rupture would as likely occur in one place as in another in such a case.

When confined in a drop of water, or in an animalcula cage, the little animals never lived as long as a minute, the field of vision was often strewn with their remains before the observer had time to look through the tube of the microscope. This was especially the case if some time had elapsed since their removal from the sea. When kept in a bucket or in any vessel containing a large quantity of water they lived for a much longer time.

Many experiments were made with destructive agents with the view of killing the animalculæ before they had time to destroy themselves, but the results were unsatisfactory. In every instance they failed to accomplish the end for which they were used; if they served any purpose it was to accelerate the process of selfdestruction.

The only explanation that I can give for this suicidal propensity lies in the abstraction of oxygen from the water; yet this appears somewhat exceptional in view of the fact that this gas is rather immaterial to the existence of the low, structureless forms of animal life. The bacteria, for instance, will flourish in infusions that have been boiled and hermetically sealed.

We have a record of these minute animals having been in this locality for more than three hundred years, defying the combined action of the winds, waves, and currents, and remaining as closely aggregated as a community of individuals endowed with reason. or instinct, and not exposed to dispersing causes. They apparently have great control over their movements, at least so far as regards the fixity of their positions.

The great Colorado River, at the head of the gulf, constantly pours into it an immense volume of water which has a tendency to carry things seaward, as it does logs and other drift; yet here. is this microscopic animal, the 1-1000 of an inch long, exposed to the same influence, but remaining in its chosen locality for centuries. What keeps these masses together forever in one place in spite of the circulation of the waters on the surface of the earth? Well might the question have presented itself to the mind of Darwin, but his fertile imagination suggested no adequate solution for it.

Other patches of discolored water obey the same impulse. In

1835 Mr. Darwin investigated that off the coast of Peru. The earliest notice we have of its existence in that locality is the beginning of the nineteenth century, and a good authority might be cited for its existence there as late as 1872. In the latter year while sailing down the eastern coast of South America we passed through a tract, while off the mouth of the Rio de la Plata, where the surface of the water was covered with a thick scum, resembling saw-dust. Darwin, in 1832, or forty years previous, found it further north, in the vicinity of the Abrolhos Islets. In this case the material that discolors the water belongs to the vegetable kingdom. It is a "minute cylindrical conferva," the Trichodesmium erythræum. According to Ehrenberg, the color of the water of the Red Sea is due to the presence of a “peculiar genus of alga," and Darwin states, on another authority, that it is the same species as that found off the coast of Brazil. In the latter locality it would certainly argue a defect of the vision to call the water red. Old sailors call it whales' feed, which, with them, is the generic title of everything that discolors the water of the ocean.

"The brick-colored and corrosive waters of certain parts of the gulf-head" received an easier solution at our hands than the more vermilion patches of the mouth of the gulf. The former is spoken of as being so extremely caustic as to remove the skin from the body like a blister, and to cause obstinate boils and ulcers, similar to those produced by scurvy, and which lasted for a long time. Some have gone so far as to even state that it would rot the clothes of those who were incautious in meddling with it. A recent compiler has endeavored to account for this peculiar property of the water on the supposition of an "excess of the iodides, bromides and sulphurets of minerals, derived, doubtless, from the abundance of volcanic material so common in these portions of the gulf." But as is common in such cases of explanatory guessing, his answer is not the true one.

Most of our information concerning this water has come down to us with the accounts of the voyages of Father Consag and Ugarte, both of whom confined their explorations, in these parts, to the head waters of the gulf; the former in 1746, and the latter in 1721.

We encountered this peculiar caustic water in about the same locality assigned it by Consag and others. In the Bay of Muleje, an indentation in the coast more than half way up the peninsula,

the whole surface of the water was of a milky-red color. The body that gives to this water the strangely caustic properties is not a mineral, but an animal—a flagellate infusorium—the common Noctiluca miliaris. In this well-sheltered bay they accumulate from their light specific gravity at the top of the water. How thick the stratum was we did not ascertain, but we may form some idea of its extent from the fact that we steamed through the tract in a straight line for four or five hours at a speed of about five knots per hour. We dipped a canvas bucket in their midst,

and when the water drained off it remained half filled with the animalculæ. They resemble minute grains of boiled sago. Every drop of water was literally crowded with them. They were so small that it required two or three to cover the area of a pin's head. It is very easy to comprehend how, if this bay were agitated by the slightest cause, it would glow as a broad sheet of living fire.

The Spanish sailors bathed in this water, and according to their chroniclers their bodies were covered with boils and ulcers in consequence. They were only half-way right when they attributed their infirmities to the water. The lashes of the little noctiluca were, undoubtedly, the exciting agents-the direct cause of their troubles; but that they were insufficient, in themselves, to account for the severity of the symptoms the evidence of our own men under different conditions of bodily health sufficiently proves. That their ulcers were similar to the effects of scurvy they recognized; and that a scorbutic condition of the blood played an important part in their production is evident. All sailors in those days were more or less the subjects of scurvy, which was a greater obstacle to the spread of commerce than were the small crafts of the navigators. It is a disease that often manifests itself in the form of boils and ulcers, and it exaggerates all trivial bruises and injuries of the skin. If our own sailors had been scorbutic when they bathed in the water the same train of symptoms would undoubtedly have followed; and, as it was, the skin, in places, became considerably inflamed and swollen, but the only disagreeable symptoms were the burning and tingling that accompanied the inflammation, which was of short duration.

NOTES ON THE DISTRIBUTION OF TIMBER IN SOUTH-WESTERN IOWA, WITH INFERENCES CONCERNING THE ORIGIN OF PRAIRIES.1

UPO

BY PROF. J. E. TODD.

PON the bluff deposit of Western Iowa is found an unusually favorable field for testing the theories concerning the muchvexed question of the origin of prairies, or rather the origin of forests, for doubtless the former are necessarily the older conditions of most regions.

The soil over wide areas is almost perfectly uniform, and so deep that no underlying formation can thrust in its influence to complicate the problem. The surface is almost infinitely varied; the high plain which is the summit of the loess, the low alluvial plains and hill-sides and bluff-sides presenting every conceivable angle of inclination, and dipping in every possible direction. To produce even greater variety, ledges of rock and knolls of gravel occasionally appear.

I.

In such a region timber occurs in the following circumstances: (1.) In the hill-regions where the slopes are inclined from 51 to 10°, it is found much the most generally on the northern slopes just south of creeks flowing east or west. This was noted some years since, by Mr. J. A. Allen.

Timber is found in the same region a little less frequently on western slopes, east of creeks flowing north or south. On the same streams considerable timber may occasionally be found on the west side. All other portions of the hill region are uniformly destitute of trees..

(2.) In the bluff region, where the slopes are from 10° to 45°, just east of the bottom lands of the Missouri river, timber is found over most of the surface, forming a belt from one to five miles in width, in Fremont county, and extending northward through Mills and Pottawattamie counties, with a narrowing and more interrupted course till it fades out in Harrison county. This belt is usually bounded on the west by the crest of the most western ridge of bluffs, leaving the slopes facing the bottom land bare, except in two well-marked cases; the first, when a lake, 1 Read before the Iowa Academy of Science, September 26, 1877.

slough or stream comes close to the base of the bluffs; the second, when the bluff-side is deeply furrowed with ravines. In the former case the slopes are covered with bushes and scrub-oaks, often quite to the top. In the latter, the ravines are wooded, usually with the trees extending considerably higher on the south side than upon the north, and often the latter is scarcely wooded at all. These points are very evident to one riding over the bottom lands so far away as to get a general view.

(3.) In the low alluvial valleys, the timber is found along the streams, usually in narrow strips, widening to fill the bends, and usually wider on the east and north sides of the stream. All other portions of the bottom lands are remarkably destitute of trees and bushes.

II.

The timbered areas are very constant, increasing very slowly if at all. This is indicated by the existence of old trees, over two hundred years old, within four or five rods of prairie, and the prairie showing no signs of having been previously timbered. Some of these cases were on the north side of groves, which side is most exposed to prairie fires, as the north-west wind usually prevails when the prairies are burning. Moreover after a personal acquaintance for the past twenty-five years with numerous localities in this region where the annual fires have been kept out, the writer has not yet learned of a single case where the advance of the timber has been more than five rods, and in the great majority of cases it has not been as many feet. He has not noted any cases of any destruction of timber by prairie fires except on the bottom lands, where the grass is much more rank and the timber is not protected by outlying hazel thickets as upon the upland. Almost the only gain of timber land is due to seeds of the cotton-wood and willow finding lodgment on the bare surface of sand bars, "break offs," and where freshets break the turf, or cover it with a layer of bare earth. From such beginnings sometimes thrifty groves result, but quite as frequently the trees so started barely hold their own against their herbaceous foes, if not assisted by the favoring hand of man. In the slow advance of groves before alluded to, the Rhus glabra takes the front rank, and the hazel follows, preparing the way for elms, hickories, etc.